Once again, thank you very much for your help and your fast response Bob. I
tried it and it works... But I still need some help. I need the concatenation
to be in a fixed cell (e.g. D12), instead of the active cell... I tried the
following code:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
With Range("D12")
.Value = Range("A1").Value & "-" & Range("C1").Value
.Characters(1, Len(Range("A1").Value)) _
.Font.Bold = True
End With

It works at first, but once I click on any cell, all the text in D12 becomes
bold. Can you do something to make it work properly... It will be great if
you can help. If you can't, it's o.k. and I'm very thankful to you for trying
helping me before.