Sub DupeCheck()
Dim i As Long
' Looping through Column B
For i = 1 To Worksheets(1).Columns(2).Rows.Count
Dim objCell As Range
Set objCell = Worksheets(1).Columns(2).Rows(i)
If Not objCell.Value = Empty Then
Dim objCellsFound As Range
' For each cell in Column B, look for it in A
Set objCellsFound = Worksheets(1).Columns(1).Find(objCell.Value)
If Not objCellsFound Is Nothing Then
' Check to see if any cells matched
If Not objCellsFound.Count = 0 Then
' Go to the row with the same number as the cell we found,
' find column "E" and put an "X" in the cell
Worksheets(1).Rows(objCellsFound.Row).Columns(6).Value = "X"
End If
End If
Next
End Sub