This does exactly what you want, based upon the screen shot you've given
Before
And after I click the "highlight the dupes" button
The top part is the bit you can customise. At the moment, I'm looking at Col A and B, but you may want to update that to look at Cols B and C or A and D etc.
I've also provided detail and a link to affect the highlight colour (again, see comments in code)
Sub HighlightDuplicates()
Dim transparent As Integer
transparent = -4142
Dim yellow As Integer
yellow = 27 ' colour index, see http://dmcritchie.mvps.org/excel/colors.htm for more details about setting the colour
Dim column1 As String
column1 = "A" 'Update me if you don't want to check for dupes in the A column
Dim column2 As String
column2 = "B" 'Update me if you don't want to check for dupes in the B column
Dim endOfRows As Boolean
moreRows = True
Dim currentCell As Integer
currentCell = 0
Do While (moreRows)
currentCell = currentCell + 1
Dim aValue As String
Dim bValue As String
aValue = Worksheets("Sheet1").Range(column1 & currentCell).Value
bValue = Worksheets("Sheet1").Range(column2 & currentCell).Value
'check it isn't already coloured
If (Worksheets("Sheet1").Range(column1 & currentCell).Interior.ColorIndex = transparent) Then
Dim moreInnerRows As Boolean
moreInnerRows = True
Dim currentInnerCell As Integer
currentInnerCell = currentCell
Dim isDupe As Boolean
isDupe = False
'Now to loop through the other rows
Do While (moreInnerRows)
currentInnerCell = currentInnerCell + 1
If (Worksheets("Sheet1").Range(column1 & currentInnerCell).Value = "" And Worksheets("Sheet1").Range(column2 & currentInnerCell).Value = "") Then
Exit Do
End If
If Worksheets("Sheet1").Range(column1 & currentInnerCell).Value = aValue And Worksheets("Sheet1").Range(column2 & currentInnerCell).Value = bValue Then
isDupe = True
Worksheets("Sheet1").Range(column1 & currentInnerCell).Interior.ColorIndex = yellow
Worksheets("Sheet1").Range(column2 & currentInnerCell).Interior.ColorIndex = yellow
End If
Loop
If (isDupe = True) Then
'Now we mark the original row as a dupe
Worksheets("Sheet1").Range(column1 & currentCell).Interior.ColorIndex = yellow
Worksheets("Sheet1").Range(column2 & currentCell).Interior.ColorIndex = yellow
End If
End If
If (Worksheets("Sheet1").Range(column1 & currentCell).Value = "" And Worksheets("Sheet1").Range(column2 & currentCell).Value = "") Then
Exit Do
End If
Loop
End Sub
Blaaah | 2 | Don't care
then I assume it's not considered a duplicate?