The effects of somatotropin (0.2 mg/kg body mass) and somatostatin (0.1 mg/kg body mass) on plasma coagulation factors II, VII, IX, X and some general indexes of hemocoagulation were examined. Hormones were injected subcutaneously in male Wistar rats on 3 consecutive days. Boehringer Mannheim tests and Schnitger and Gross coagulometer were used for clotting factor determination. Somatotropin caused significantly decreased activity of factors II, VII and X (P < 0,001) and IX (P < 0.05). Somatostatin alone, as well as somatotropin after somatostatin pretreatment considerably increased the activity of factors II, VII and X (P < 0.001), while factor IX was non-significantly suppressed. It is concluded that somatotropin and somatostatin are possible regulators of biosynthesis of vitamin K-dependent plasma coagulation factors. Somatotropin depresses the activity of factors II, VII, IX and X and causes hypocoagulability, while somatostatin not only prevents the inhibiting effect on factors II, VII and X, but also increases their activity and causes hypercoagulability.