The aim of our study was the assessment whether internal peroxidase of arachidonic acid and/or prostaglandin can be transferred from platelets to monocytes. Monocytes were isolated from whole blood according to the method of Böyum. The monocytes cultures were led in the fluid environment, on the base of RPMI 1640 supplemented with autologous serum. Platelets were isolated from whole blood according to the method of Pinckard. During interaction of monocytes and platelets in the presence of indometacin we ascertained the increased of TXB2 concentrations in supper-natant. Incubation of monocytes in cultures stimulated by LPS in presence of indomethacin with platelets did not cause increased secretion of TXB2. Incubation of platelets with indomethacin in 36 h culture of monocytes stimulated by LPS caused increase concentration of 6-keto-PGF1alfa. The results of our study may suggest the presence of the one way transformation of the arachidonic acid from platelets to monocytes.