The implementation of FPROLOG - a fuzzy PROLOG interpreter. One of the shortcomings of PROLOG, widely used in artificial intelligence research is its failure of manipulating uncertain reasoning. The authors propose the elimination of this constraint by replacing the conventional two-valued logic PROLOG is based upon, with fuzzy logic. In order to give greater flexibility to the system, the fuzzy PROLOG interpreter can be linked with the FRIL system, yielding a powerful language for knowledge representation.