This paper discusses incorporating C (and FORTRAN) functions into the XLISP-STAT statistical computing environment, by using shared libraries loaded at runtime. We provide a number of examples that can be used as templates. They can be used (as in S-plus) to speed up XLISP-STAT programs, but also (as in SWIG) to produce graphical user interfaces for existing C and FORTRAN programs. The appendices discuss a number of completed projects following these lines which considerably extend XLISP-STAT.