Sub dedupe_abcd()
    Dim icol As Long

    With Sheets("Sheet1")   '<-set this worksheet reference properly!
        icol = Application.Match("abcd", .Rows(1), 0)
        With .Cells(1, 1).CurrentRegion
            .RemoveDuplicates Columns:=icol, Header:=xlYes
        End With
    End With
End Sub