USED() will work, but if you have multiple data sessions going USED() will only return for that data session and if you know the table alias. If you require more than that you will need to write your own function that loops through all data sessions and checks the table at a low level for use and returns that instance of an alias and session number so you can get a handle on it or close it for re-opening. We had to do this so we could open tables exclusive on occasion for re-indexing and such...