Private Sub Worksheet_Change(ByVal Target As Range)
Const WS_RANGE As String = "H:H" '<=== change to suit

On Error GoTo ws_exit:
Application.EnableEvents = False
If Not Intersect(Target, Me.Range(WS_RANGE)) Is Nothing Then
With Target
If Application.CountIf(Range(WS_RANGE), .Value) 1 Then
MsgBox "Duplicate value"
.Value = ""
End If
End With
End If

ws_exit:
Application.EnableEvents = True
End Sub

'This is worksheet event code, which means that it needs to be
'placed in the appropriate worksheet code module, not a standard
'code module. To do this, right-click on the sheet tab, select
'the View Code option from the menu, and paste the code in.


--
HTH

Bob Phillips

(replace somewhere in email address with gmail if mailing direct)

"Edna" wrote in message
...
How do I create a macro to avoid duplicating a number in a column