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A comparative analysis of the temperature effect on the thrombin- and trypsin-catalyzed hydrolysis of synthetic substrates which are derivatives of A(alpha)-chain of fibrinogen has been carried out. The substrates have general formula: Tos-P2-Arg-OCH3 and Tos-P3-P2-Arg-OCH3, where P2-Gly, Val, MeVal; P3 = Gly, Sar. The activation parameters delta G not equal to, delta H not equal to and delta S not equal to are determined. Thrombin is shown to split the most effectively tripeptide containing amino acids sequence Gly-Gly at the subsites of P3 and P2. It is suggested to be caused by an ability of the above compound to take a bent conformation at the active site of thrombin.