I am working on a macro in Microsoft Excel 2000 vba.

I want to concatenate the two cells to the left of it.

This is what I have so far:

ActiveCell.FormulaR1C1 = "=CONCATENATE(RC[-2],RC[-1])"
Range("E4").Select
Selection.AutoFill Destination:=Range("E4:E6")
Range("E4:E6").Select
Range("E7").Select
End Sub

How do I run the same macro, but have it check to the cell left of it?

If the cell to the left of it has a value in it, I want it to
concatenate.

If the cell is a *null* or *blank cell*, I want the sub to stop.

How do I do it?

Thank you in advance for your help.