"jose luis " wrote...
I´m trying to prevent a file to run in a Mac system (OS 9 , OS X)
Could you give a hint on how to detect this situation to impede the
user to run the app?

You could use Application.OperatingSystem in a Workbook_Open event handler,
but it wouldn't work if users disable macros. Unless your workbook mainly
runs macros, there's no way to prevent it from running on Macs.