This book contains the proceedings of a symposium on the use of synthetic substrates in clinical blood coagulation assays, which was held at the University of Leuven, Belgium, on March 1st, 1980. This meeting was organized in order to exchange and discuss recent develop­ ments and applications in this field. Advantages and disadvantages of synthetic substrates are discussed, while expert workers report on their practical experience with the use of chromogenic substrates in routine assays for blood coagulation and fibrinolysis. The indications when to perform antithrombin III, a2-antiplasmin, factor X and factor II determinations are discussed. For each of the determinations a critical evaluation of the chromogenic assay as compared to the classical assay is presented. The clinical relevance of these assays for anticoagulated and cirrhotic patients, detection of vitamin K deficiency, monitoring heparin therapy and the fibrinolytic system are discussed. Recent developments in the use of fluorogenic substrates for the assay of low concentrations of fibrin­ olytic activators are presented. Taking into account all practical, medical and economical con­ siderations an answer is prepared to the question "Are synthetic sub­ strates to be recommended for routine use?". To make this symposium useful, rapid publication of the proceedings has been undertaken. We are grateful to the participants in this meeting for their co­ operation and for their willingness to provide manuscripts of their presentations. The manuscripts provided by C. Kluft and H.H.D.M.