An insulin-heparin complex was obtained in vitro. The hypoglycemic effect of insulin, included into this complex as compared with free insulin, was increased more than 2-fold when it was tested in animals with stable alloxane diabetes. Contrary to insulin, administration of the insulin-heparin complex increased the anticoagulation properties of blood and exhibited the non-enzymatic fibrinolytic activity towards the unstabilized fibrin both in presence or in absence of inhibitors of fibrinolysis, caused by plasmin.