Overall 16 patients with chronic renal failure on regular hemodialysis were examined. Of these, 8 received recombinant human erythropoietin (rhERP). A study was made of platelet aggregation and the level of some prostanoids in the blood of these patients. As the time of the treatment with rhERP was increased, the hemodialyzed patients demonstrated a tendency toward a rise of platelet aggregation induced by thrombin together with an increase of the content of PGF2 alpha, TxB2, in some cases of 6-keto-PGF1 alpha and a lowering of plasma PGE [correction of RGE] level. The data concerning activation of the synthesis of arachidonic acid metabolites (PGF2 alpha and TxB2) that enhance platelet aggregation on prolonged use of rhERP suggest the role these substances may play in the mechanism of the development of thrombotic complications in the given patients' category.