The proposed research will focus upon the development and evaluation of a model proteinase inhibitor. This model will be a small synthetic peptide designed to mimic the active site region of basic pancreatic trypsin inhibitor (BPTI), a clinically useful protein which inhibits several serine proteinases. Established principles of peptide conformation, used in the design of the proposed inhibitor, indicate that it will bear a strong conformational resemblance to the BPTI active site. It should, therefore, possess similar inhibitory properties. Both the conformation of the proposed inhibitor and its interactions with a spectrum of serine proteinases will be carefully examined. The strategy adopted for the synthesis of the model inhibitor will also make it possible to elaborate a number of potentially interesting analogs. Some of these analogs will be formulated so as to express new inhibitory specificities not found in BPTI. A major study of this type will be an attempt to design an inhibitor of thrombin or the thrombokinetic pathway. If successful this would represent not only the development of a new molecule of possible clinical value but also the demonstration of the practicability of this new approach to drug design.