Peptide synthesis is an important research tool. However, successful syntheses require considerable effort from the scientist. We have produced an expert System, the PepPro Peptide Synthesis Expert System, that helps the scientist improve peptide syntheses. To use PepPro the scientist enters the peptide to be synthesized. Peppro then applies its synthesis rules to analyze the peptide, to predict coupling. problems, and to recommend solutions. PepPro produces a synthesis report that summarizes the analysis and recommendations. The program includes a capability that allows the scientist to write new synthesis rules and add them to the PepPro knowledge base. PepPro was developed on Xerox 11xx series workstations using Beckman’s proprietary development environment 0"). We then compiled PepPro to run on the IBM PC. PepPro has limitations that derive from unpredictable events during a synthesis. Despite the limitations, PepPro provides several important benefits. The major one is that it makes peptide syntheses easier, less time-consuming, and more efficient.