My read was that you wanted to have it deny duplicate entries 'as they are
typed' similar to the Data Validation feature except that the latter allows
you to specify only what is allowed as opposed to what is denied.

Paste the following to the worksheet code module:-
Private Sub Worksheet_Change(ByVal Target As Range)
Dim rng1 As Range, rng2 As Range
Dim ws2 As Worksheet
Dim c As Range
Dim Msg As String, Title As String

Set ws2 = Sheets("Sheet2")
Set rng1 = Me.Columns(1)
Set rng2 = ws2.Range(ws2.Range("A1"), _
ws2.Range("A1").End(xlDown))
If Target.Count 1 Then Exit Sub
Title = "Data Validation"
If Not Intersect(Target, rng1) Is Nothing Then
Set c = rng2.Find(Target.Value, , , xlWhole)
If Not c Is Nothing Then
With Target
..Select
Msg = "Entry denied !!!" & vbCr & vbCr & _
"The word """ & .Value & _
""" already exists on " & rng2.Parent.Name & ". "
MsgBox Msg, vbCritical, Title
..ClearContents
End With
End If
End If
Set rng1 = Nothing
Set rng2 = Nothing
Set c = Nothing
End Sub

Regards,
Greg


"ChristalClarity" wrote:

I want to structure a macro that will automatically search entries in a
colunm on worksheet A, compare those entries to a column in spreadsheet B and
then disallow the entry if there is a match.