The water-methanol phase products obtained by slight alkali deacylation of a phosphatidyl-ethanolamine and phosphatidyl serine mixture, reveal a higher specific anticoagulating activity than the base mix. In the composition of the water-methanol phase glycerin, serine, ethanolamine, phosphoryl-serine, phosphoryl-ethanolamine, glyceryl-phosphoryl-ethanolamine and glyceryl-phosphoryl-serine were detected by the method of thin-layer paper chromatography. The only substance, glycerly-phosphoryl-serine, possesses an inhibitory activity. Therefore, anticoagulative activity of phosphatidyl-serine is not connected with the presence of the fatty acid residue in its molecule, it is due to the glyceryl-phosphoryl-serine residue. The further glyceryl-phosphoryl-serine degradation is accompanied by the disappearance of the anticoagulative activity.