SummaryA new generation of specific and sensitive substrates for enzymes has been developed; they consist of a peptide moiety and a chromophoric leaving group, usually p-nitroanilide. The rate of release of p-nitroaniline from this type of substrate is proportional to the enzymatic activity, and can be measured spectrophotometrically from the increase in the absorbancy at 405 nm per unit of time. The specificity of these chromogenic substrates is determined by the nature and the sequence of their amino acids. Possible applications of these substrates in the field of blood coagulation and fibrinolysis include the monitoring of heparin therapy, oral anticoagulant therapy and thrombolytic therapy. The clinical value of a number of these chromogenic substrate assays is still under investigation.