The influence of 2-morpholino-5-(thienyl-2)-6-H-1,3,4-thiadiazine (H-29) on the platelet aggregation has been studied in experiments on donor plasma in vitro. It is established that H-29 causes a decrease in the platelet interaction induced by ADP and arachidonic acid. The influence of H-29 on platelet aggregation was also studied in ex vivo experiments with intravenous and oral administration, and some parameters of plasmatic hemostasis were evaluated.