Quaternary ammonium salt of oligomer-25 conidine (QAS O-25C) was used for regulation of hypocoagulation effect of Syncumar--anticoagulant of indirect type of action. The experiments were carried out on male rats. Experimental methods included thromboelastography, determination of thromboplastin time (after Quick) and determination of activity of single coagulation factors. It was shown that injection of QAS O-25C reliably do not affect blood coagulation. The combined action of QAS O-25C and Syncumar resulted in a twofold increase in the activity of factors IX and X within 24 h after the injection and in complete recovery after 48 h. After Syncumar injection per os we observed deep-hypercoagulation which was maintained even within 48 after the injection. The effect of QAS O-25C modulating the Syncular anticoagulant activity is probably connected with intensification of protein synthesis in the liver and, specifically, with an increase in the yield of active precursors of the factors of prothrombin complex.