doublons

Private Sub CommandButton1_Click()
 Dim c As Range, a As Variant
 For Each c In Range("a1", Cells(Rows.Count, "a").End(xlUp))
 Set a = [a:a].Find(What:=TextBox1.Value, LookIn:=xlValues, LookAt:=xlWhole)
If Not a Is Nothing Then MsgBox " doublons": Exit Sub Else 'autre action
 Next
End Sub

Private Sub CommandButton1_Click()
If Application.CountIf([A:A], Textbox1) Then
  MsgBox "doublons"
  Textbox1 = ""
  Textbox1.SetFocus 'donne le focus
  Exit Sub
End If
'suite du code
End Sub