Sub test()
Dim i As Byte, k As Integer, val As Variant
Application.ScreenUpdating = False
Workbooks('ancien.xls').Activate
For i = 3 To Range('A65536').End(xlUp).Row
val = Cells(i, 1).Value
If not Workbooks('Nouveaux.xls').Sheets(1).Cells(i, 1).Value = val Then
Workbooks('Nouveaux.xls').Sheets(1).Cells(i, 1).Font.ColorIndex = 40
For k = 2 To Range('IV' & i).End(xlToLeft).Column
If not Workbooks('Nouveaux.xls').Sheets(1).Cells(i, k).Value = Cells(i, k).Value Then
Workbooks('Nouveaux.xls').Sheets(1).Cells(i, k).Font.ColorIndex = 40
End If
Next k
End If
Next i
Application.ScreenUpdating = True
End Sub