diff --git a/backend/nodes/multi_profile.py b/backend/nodes/multi_profile.py
index 77a6763..c000f23 100644
--- a/backend/nodes/multi_profile.py
+++ b/backend/nodes/multi_profile.py
@@ -5,7 +5,23 @@ from __future__ import annotations
 import numpy as np
 
 from backend.node_registry import register_node
-from backend.data_types import DataField, LineData
+from backend.data_types import DataField, LineData, datafield_to_uint8, encode_preview
+from backend.execution_context import emit_overlay
+
+
+def _blend_fields(field_a: DataField, field_b: DataField, alpha: float) -> np.ndarray:
+    """Render field A with field B overlaid at `alpha` opacity (0=A only, 1=B only)."""
+    a_rgb = datafield_to_uint8(field_a, field_a.colormap).astype(np.float32)
+    b_rgb = datafield_to_uint8(field_b, field_b.colormap).astype(np.float32)
+    wa = 1.0 - alpha
+    wb = alpha
+    if b_rgb.shape != a_rgb.shape:
+        h = min(a_rgb.shape[0], b_rgb.shape[0])
+        w = min(a_rgb.shape[1], b_rgb.shape[1])
+        canvas = a_rgb.copy()
+        canvas[:h, :w] = wa * a_rgb[:h, :w] + wb * b_rgb[:h, :w]
+        return canvas.astype(np.uint8)
+    return (wa * a_rgb + wb * b_rgb).astype(np.uint8)
 
 
 @register_node(display_name="Multiple Profiles")
@@ -19,11 +35,12 @@ class MultipleProfiles:
                 "row": ("INT", {"default": -1, "min": -1, "max": 10000, "step": 1}),
                 "direction": (["horizontal", "vertical"], {"default": "horizontal"}),
                 "mode": (["overlay", "mean", "difference"], {"default": "overlay"}),
+                "blend": ("FLOAT", {"default": 0.5, "min": 0.0, "max": 1.0, "step": 0.01, "slider": True}),
             }
         }
 
     OUTPUTS = (
-        ('LINE_DATA', 'profile'),
+        ('LINE', 'profile'),
     )
     FUNCTION = "process"
 
@@ -31,12 +48,14 @@ class MultipleProfiles:
         "Extract and compare line profiles from two fields. "
         "Row=-1 uses the center row/column. Modes: overlay returns field_a's "
         "profile, mean averages both, difference subtracts b from a. "
+        "The preview shows field A blended with field B and highlights the "
+        "row or column being sampled — drag to move the line."
     )
 
     KEYWORDS = ("line profile", "compare", "overlay", "cross section")
 
     def process(self, field_a: DataField, field_b: DataField,
-                row: int, direction: str, mode: str) -> tuple:
+                row: int, direction: str, mode: str, blend: float = 0.5) -> tuple:
         a = np.asarray(field_a.data, dtype=np.float64)
         b = np.asarray(field_b.data, dtype=np.float64)
 
@@ -49,6 +68,7 @@ class MultipleProfiles:
             pa = pa[:len(pb)]
             dx = field_a.dx
             x_unit = field_a.si_unit_xy
+            line_axis_max = a.shape[0] - 1
         else:
             if row < 0:
                 row = a.shape[1] // 2
@@ -58,6 +78,7 @@ class MultipleProfiles:
             pa = pa[:len(pb)]
             dx = field_a.dy
             x_unit = field_a.si_unit_xy
+            line_axis_max = a.shape[1] - 1
 
         x_axis = np.arange(len(pa)) * dx
 
@@ -70,5 +91,15 @@ class MultipleProfiles:
         else:
             result = pa
 
+        alpha = float(np.clip(blend, 0.0, 1.0))
+        emit_overlay({
+            "kind": "multi_profile",
+            "section_title": "Preview",
+            "image": encode_preview(_blend_fields(field_a, field_b, alpha)),
+            "row": int(row),
+            "direction": direction,
+            "max_index": int(line_axis_max),
+        })
+
         return (LineData(data=result, x_axis=x_axis, x_unit=x_unit,
                          y_unit=field_a.si_unit_z),)
diff --git a/docs/nodes/Multiple Profiles.md b/docs/nodes/Multiple Profiles.md
index 84a905e..388b2ae 100644
--- a/docs/nodes/Multiple Profiles.md	
+++ b/docs/nodes/Multiple Profiles.md	
@@ -1,6 +1,6 @@
 # Multiple Profiles
 
-Extract and compare line profiles from two fields along a chosen row or column. Supports overlay, mean, and difference modes. Equivalent to Gwyddion's multiprofile.c module.
+Extract and compare line profiles from two fields along a chosen row or column. Supports overlay, mean, and difference modes.
 
 ## Inputs
 
@@ -13,7 +13,7 @@ Extract and compare line profiles from two fields along a chosen row or column.
 
 | Name | Type | Description |
 |------|------|-------------|
-| profile | LINE_DATA | Resulting line profile |
+| profile | LINE | Resulting line profile |
 
 ## Controls
 
@@ -22,6 +22,11 @@ Extract and compare line profiles from two fields along a chosen row or column.
 | row | INT | -1 | Row (horizontal) or column (vertical) index to extract; -1 uses the centre row/column (-1-10000) |
 | direction | dropdown | horizontal | Profile direction: horizontal (extract a row) or vertical (extract a column) |
 | mode | dropdown | overlay | Combination mode: overlay (field_a profile only), mean (average of both), or difference (field_a minus field_b) |
+| blend | FLOAT | 0.5 | Opacity of field B in the preview (0 = only A, 1 = only B). Affects the preview image only, not the extracted profile. |
+
+## Interactive preview
+
+The preview shows field A blended with field B and highlights the row or column being sampled. Click or drag on the image to move the line; switch between row and column extraction with the `direction` control.
 
 ## Notes
 
diff --git a/frontend/src/CustomNode.tsx b/frontend/src/CustomNode.tsx
index e07710f..0c8860f 100644
--- a/frontend/src/CustomNode.tsx
+++ b/frontend/src/CustomNode.tsx
@@ -14,6 +14,7 @@ const AngleMeasureOverlay = lazy(() => import('./AngleMeasureOverlay'));
 const ThresholdHistogram = lazy(() => import('./ThresholdHistogram'));
 const RadialProfileOverlay = lazy(() => import('./RadialProfileOverlay'));
 const StraightenPathOverlay = lazy(() => import('./StraightenPathOverlay'));
+const MultiProfileOverlay = lazy(() => import('./MultiProfileOverlay'));
 
 import TextNoteNode from './TextNoteNode';
 
@@ -1198,6 +1199,7 @@ function CustomNode({ id, data }: { id: string; data: NodeData }) {
     || data.overlay.kind === 'threshold_histogram'
     || data.overlay.kind === 'radial_profile'
     || data.overlay.kind === 'straighten_path'
+    || data.overlay.kind === 'multi_profile'
   );
   const hidePreviewForInteractiveMask = data.overlay?.kind === 'mask_paint' || data.overlay?.kind === 'markup';
   const overlayTitle = data.overlay?.section_title
@@ -1217,6 +1219,8 @@ function CustomNode({ id, data }: { id: string; data: NodeData }) {
         ? 'Radial Profile'
       : data.overlay?.kind === 'straighten_path'
         ? 'Path'
+      : data.overlay?.kind === 'multi_profile'
+        ? 'Preview'
       : 'Cross Section');
   const headerMeta = (() => {
     if (data.className === 'Folder') {
@@ -1572,6 +1576,15 @@ function CustomNode({ id, data }: { id: string; data: NodeData }) {
                   nodeId={id}
                   onWidgetChange={ctx!.onWidgetChange}
                 />
+              ) : data.overlay!.kind === 'multi_profile' ? (
+                <MultiProfileOverlay
+                  image={data.overlay!.image ?? ''}
+                  row={(data.overlay!.row ?? 0) as number}
+                  direction={(data.overlay!.direction ?? 'horizontal') as 'horizontal' | 'vertical'}
+                  maxIndex={(data.overlay!.max_index ?? 0) as number}
+                  nodeId={id}
+                  onWidgetChange={ctx!.onWidgetChange}
+                />
               ) : data.overlay!.kind === 'angle_measure' ? (
                 <AngleMeasureOverlay
                   image={data.overlay!.image ?? ''}
diff --git a/frontend/src/MultiProfileOverlay.tsx b/frontend/src/MultiProfileOverlay.tsx
new file mode 100644
index 0000000..26c6784
--- /dev/null
+++ b/frontend/src/MultiProfileOverlay.tsx
@@ -0,0 +1,89 @@
+import React, { useRef, useState, useCallback, useEffect } from 'react';
+import { clamp, pointerToFraction } from './overlayUtils';
+
+export const CAPTURE_SELECTOR = '.multiprofile-overlay';
+
+interface MultiProfileOverlayProps {
+  image: string;
+  row: number;
+  direction: 'horizontal' | 'vertical';
+  maxIndex: number;
+  nodeId: string;
+  onWidgetChange: (nodeId: string, name: string, value: unknown) => void;
+}
+
+export default function MultiProfileOverlay({
+  image, row, direction, maxIndex,
+  nodeId, onWidgetChange,
+}: MultiProfileOverlayProps) {
+  const containerRef = useRef<HTMLDivElement>(null);
+  const [draftRow, setDraftRow] = useState<number | null>(null);
+  const draggingRef = useRef(false);
+  const pendingCommitRef = useRef<number | null>(null);
+
+  useEffect(() => {
+    if (pendingCommitRef.current !== null && row === pendingCommitRef.current) {
+      pendingCommitRef.current = null;
+      setDraftRow(null);
+    }
+  }, [row]);
+
+  const displayRow = draftRow ?? row;
+
+  const fractionFromEvent = useCallback((e: React.PointerEvent<Element>): number => {
+    if (!containerRef.current) return 0;
+    const { fx, fy } = pointerToFraction(e, containerRef.current);
+    return direction === 'horizontal' ? fy : fx;
+  }, [direction]);
+
+  const fractionToIndex = useCallback((frac: number): number => {
+    return clamp(Math.round(frac * maxIndex), 0, maxIndex);
+  }, [maxIndex]);
+
+  const onPointerDown = useCallback((e: React.PointerEvent<Element>) => {
+    e.stopPropagation();
+    e.preventDefault();
+    (e.currentTarget as HTMLElement).setPointerCapture(e.pointerId);
+    draggingRef.current = true;
+    setDraftRow(fractionToIndex(fractionFromEvent(e)));
+  }, [fractionFromEvent, fractionToIndex]);
+
+  const onPointerMove = useCallback((e: React.PointerEvent<Element>) => {
+    if (!draggingRef.current) return;
+    setDraftRow(fractionToIndex(fractionFromEvent(e)));
+  }, [fractionFromEvent, fractionToIndex]);
+
+  const onPointerUp = useCallback(() => {
+    if (draggingRef.current && draftRow !== null) {
+      pendingCommitRef.current = draftRow;
+      onWidgetChange(nodeId, 'row', draftRow);
+    }
+    draggingRef.current = false;
+  }, [draftRow, nodeId, onWidgetChange]);
+
+  const fracPos = maxIndex > 0 ? displayRow / maxIndex : 0;
+  const linePct = clamp(fracPos * 100, 0, 100);
+
+  const lineStyle: React.CSSProperties = direction === 'horizontal'
+    ? { left: 0, right: 0, top: `${linePct}%`, height: 0 }
+    : { top: 0, bottom: 0, left: `${linePct}%`, width: 0 };
+
+  const cursorClass = direction === 'horizontal' ? 'cursor-row' : 'cursor-col';
+
+  return (
+    <div
+      ref={containerRef}
+      className={`nodrag nowheel multiprofile-overlay ${cursorClass}`}
+      onPointerDown={onPointerDown}
+      onPointerMove={onPointerMove}
+      onPointerUp={onPointerUp}
+      onLostPointerCapture={onPointerUp}
+    >
+      <img src={image} alt="A blended with B" draggable={false} className="multiprofile-image" />
+      <div className={`multiprofile-line multiprofile-line-${direction}`} style={lineStyle} />
+      <div className="multiprofile-readout">
+        {direction === 'horizontal' ? 'row' : 'col'} {displayRow}
+      </div>
+    </div>
+  );
+}
diff --git a/frontend/src/styles.css b/frontend/src/styles.css
index 27d0f67..c49e75b 100644
--- a/frontend/src/styles.css
+++ b/frontend/src/styles.css
@@ -1736,6 +1736,43 @@ html, body, #root {
   transform: translate(-50%, -50%) scale(1.2);
 }
 
+/* ── Multi Profile overlay ────────────────────────────────────────── */
+.multiprofile-overlay {
+  position: relative;
+  user-select: none;
+  touch-action: none;
+  overflow: hidden;
+}
+.multiprofile-overlay.cursor-row { cursor: row-resize; }
+.multiprofile-overlay.cursor-col { cursor: col-resize; }
+.multiprofile-image {
+  width: 100%;
+  display: block;
+}
+.multiprofile-line {
+  position: absolute;
+  pointer-events: none;
+}
+.multiprofile-line-horizontal {
+  border-top: 1.5px solid var(--marker);
+  box-shadow: 0 0 4px var(--marker-shadow);
+}
+.multiprofile-line-vertical {
+  border-left: 1.5px solid var(--marker);
+  box-shadow: 0 0 4px var(--marker-shadow);
+}
+.multiprofile-readout {
+  position: absolute;
+  top: 4px;
+  left: 4px;
+  font-size: 10px;
+  background: rgba(0, 0, 0, 0.55);
+  color: #fff;
+  padding: 2px 5px;
+  border-radius: 3px;
+  pointer-events: none;
+}
+
 .angle-overlay {
   --angle-line-color: #ff9800;
   --angle-arc-color: rgb(255, 166, 77);
@@ -1992,7 +2029,8 @@ html, body, #root {
 .is-panning .mask-paint-overlay,
 .is-panning .markup-overlay,
 .is-panning .radial-overlay,
-.is-panning .straighten-overlay {
+.is-panning .straighten-overlay,
+.is-panning .multiprofile-overlay {
   pointer-events: none;
 }
 
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index d14e3af..a6bed64 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -79,6 +79,9 @@ export interface OverlayData {
   thickness?: number;
   xres?: number;
   yres?: number;
+  row?: number;
+  direction?: 'horizontal' | 'vertical';
+  max_index?: number;
   section_title?: string;
   line?: number[];
   shape?: string;
diff --git a/frontend/src/workflowCapture.ts b/frontend/src/workflowCapture.ts
index 5c40bd0..9eeaafa 100644
--- a/frontend/src/workflowCapture.ts
+++ b/frontend/src/workflowCapture.ts
@@ -13,6 +13,7 @@ export const OVERLAY_CAPTURE_SELECTORS = [
   '.angle-overlay',      // AngleMeasureOverlay
   '.radial-overlay',     // RadialProfileOverlay
   '.straighten-overlay', // StraightenPathOverlay
+  '.multiprofile-overlay', // MultiProfileOverlay
 ];
 
 function encodeBase64(bytes: Uint8Array) {
diff --git a/tests/node_tests/multi_profile.py b/tests/node_tests/multi_profile.py
index b56e916..52b1cff 100644
--- a/tests/node_tests/multi_profile.py
+++ b/tests/node_tests/multi_profile.py
@@ -31,3 +31,41 @@ def test_vertical_direction():
     field = make_field(shape=(80, 40))
     (profile,) = node.process(field, field, row=-1, direction="vertical", mode="overlay")
     assert len(profile.data) == 80, f"Vertical profile length should be field height (80), got {len(profile.data)}"
+
+
+def test_emits_blended_overlay():
+    from backend.execution_context import active_node, execution_callbacks
+    from backend.nodes.multi_profile import MultipleProfiles
+
+    node = MultipleProfiles()
+    field = make_field(shape=(64, 128))
+
+    overlays = []
+    with execution_callbacks(overlay=lambda nid, d: overlays.append(d)), active_node("test"):
+        node.process(field, field, row=10, direction="horizontal", mode="overlay")
+
+    assert len(overlays) == 1
+    ov = overlays[0]
+    assert ov["kind"] == "multi_profile"
+    assert ov["section_title"] == "Preview"
+    assert ov["image"].startswith("data:image/png;base64,")
+    assert ov["row"] == 10
+    assert ov["direction"] == "horizontal"
+    assert ov["max_index"] == 63  # height - 1
+
+
+def test_overlay_max_index_for_vertical():
+    from backend.execution_context import active_node, execution_callbacks
+    from backend.nodes.multi_profile import MultipleProfiles
+
+    node = MultipleProfiles()
+    field = make_field(shape=(80, 40))
+
+    overlays = []
+    with execution_callbacks(overlay=lambda nid, d: overlays.append(d)), active_node("test"):
+        node.process(field, field, row=-1, direction="vertical", mode="overlay")
+
+    ov = overlays[0]
+    assert ov["direction"] == "vertical"
+    assert ov["max_index"] == 39  # width - 1
+    assert ov["row"] == 20  # center column for 40 wide