use the sheet's change method ....right click the sheet tab and select View
Code from the pop-up menu

Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = Range("a2").Address Then
If Range("a1") = "" Then
MsgBox "A1 is empty"
Application.EnableEvents = False
Target.Value = ""
Application.EnableEvents = True
End If
End If
End Sub


"Link" wrote in message
...
In a worksheet where you have to fill in information what formula to use
if
you want to make sure (example cell A1 is filled in before A2) In other
words
they if A1 is not filled in you cant move to A2.