CornedBee is correct. Without the .def file, the function will export, but it will shows up as its mangled name. The def file exports the function name UNmangled, and thus makes it a bit easier to use. If you are using implicit linking, this is a moot point, since only the compiler cares what the functions are called, but if you need to call the function from another language, using the def file makes things a bit easier.

Z.