Experiments on rabbits have demonstrated the ability of delagil to slightly increase the time of whole blood coagulation upon a single parenteral injection. On the contrary, prolonged administration of the drug per os and intramuscularly was accompanied by an insignificant enhancement of hemocoagulation. Delagil changed the effect of heparin administered after it. Heparin injection at the height of blood delagil content was accompanied by a decrease in specific activity of the anticoagulant. Prolonged administration of delagil potentiated the anticoagulation effect of heparin and prevented the development of the "return effect". In experiments made in vitro, delagil was found to be capable of inhibiting blood coagulation and forming complexes with heparin, which was accompanied by the loss of the anticoagulant activity of the latter. Interaction of the antimalarial agent with heparin in blood plasma and buffer medium is governed by exponential dependence.