Thankyou for your answers, it gave me some tip about where to find functions and examples in the FoxPro help manual. I think that the NVL() function will suit me best, because I only have a few characterstrings in my program which is joined with fields that can contain a NULL value.
(In other cases, I use SET NULLDISPLAY TO '' to handle fields with Null values.)

Thanks again
/Kjell