>Ok, this is sort of strange, but I need to replace values in a field only when they are truly empty. If the value is .T. or .F., then I want to leave it alone and not replace it. Sounds weird, but this is an import to a table from an excel spreadsheet and the values will either be .F. or empty. I need to change all the empty ones to .T., but not affect the ones that already have a .F. in them.

Use ISBLANK() function for your test.