GS expressed precisely :
Your code took 46 secs to run your sample data on my machine. That's amazing!
I'm curious, now, how it performs if we did similar using a Collection so we
can have duplicates in ColA!

I modified my sub to use your idea to use Dictionary, but NOT put colA
in a dictionary and it shaved 11 secs off the ET...

Sub StripDupes()
Dim i&, j&, lRows1&, lRows2& lMatchesFound& 'as long
Dim vRngA, vRngB, vRngOut() 'as variant
Dim dRngB As Dictionary

lRows1 = Cells(Rows.Count, "A").End(xlUp).Row
lRows2 = Cells(Rows.Count, "B").End(xlUp).Row
vRngA = Range("A1:A" & lRows1): vRngB = Range("B1:B" & lRows2)

Set dRngB = New Dictionary
Debug.Print Now()
For j = LBound(vRngB) To UBound(vRngB)
With dRngB
If Not .Exists(Key:=vRngB(j, 1)) Then _
.Add Key:=vRngB(j, 1), Item:=vRngB(j, 1)
End With
Next 'j
sTemp = Mid$(sTemp, 2)
' Debug.Print Now()

For i = LBound(vRngA) To UBound(vRngA)
If dRngB.Exists(Key:=vRngA(i, 1)) Then _
vRngA(i, 1) = "": lMatchesFound = lMatchesFound + 1
Next 'i
' Debug.Print Now()

j = 0: ReDim vRngOut(UBound(vRngA) - lMatchesFound, 1 To 1)
For i = LBound(vRngA) To UBound(vRngA)
If Not vRngA(i, 1) = "" Then
vRngOut(j, 1) = vRngA(i, 1): j = j + 1
End If
Next 'i
' Debug.Print Now()

Range("A1:A" & lRows1).ClearContents
Range("A1").Resize(UBound(vRngOut), 1) = vRngOut

Debug.Print Now()
End Sub

--
Garry

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