Hemostatic measurements were undertaken in eight chronic hemodialysis uremic patients on recombinant human erythropoietin (rHuEpo). Same measurements were repeated in another seven patients in whom anemia was corrected by the transfusion of red blood cells. The correction of the anemia by rHuEpo therapy was accompanied by 1. correction of the prolonged Simplate Bleeding Time (BT) to normal less than 10.0, minutes after 16 weeks of rHuEpo treatment; 2. significant increases in the levels of fibrinogen, clotting FVIII:C, vWF:antigen, vWF:ristocetin cofactor and platelet count; 3. enhanced aggregation responses to ADP, adrenaline, arachidonic acid, collagen and ristocetin. There was no significant fluctuation in other coagulation parameters PT, APTT, TT, reptilase time and antithrombin III and plasma fibrinogen. In patients who were treated with RBC transfusion and despite the correction of the anemia, the bleeding time shortened significantly but not corrected, mean BT before and after RBC transfusion was 17.1 +/- 1.4 and 11.6 +/- 1.9 minutes respectively. Besides there was significant elevation of vWF:Ricofactor levels but not FVIII:C, vWF:Ag or platelet count. Platelet aggregation responses to ADP remained unchanged. It is concluded that significant elevations of FVIII:related activities, plasma fibrinogen, improved platelet aggregability and correction of the BT are salient hemostatic changes that follow rHuEpo therapy in uremic patients.