I am currently developing a set of applications in C under MPE. This software will need to have approximately 150 variations for different clients. These variations will be small (say - 1% of the entire application). The approach I have taken is to have 1 main program where 99% of the code resides, and a small executable library (XL) for each client. The XL will have 1 function - Custom() containing all of the client specific code. I will always be running the same program, but linking in a different custom XL at runtime. run mainprog;xl="custom1.xl" run mainprog;xl="custom2.xl" run mainprog;xl="custom3.xl" etc This is working, but now my problem: Once I am inside the Custom() function in the XL I would like to be able to call functions back in the mainprog. I cannot get this to work, because any attempt at calling a function in mainprog results in an unresolved external. I understand why I am getting this, but is there any way to get this to work? Any comments, ideas, or suggestions would be appreciated. Ken Hood Trans Union of Canada [log in to unmask]