The authors evaluated the behavior of protein C activity, factor X and factor VII coagulant activity and serum lipoprotein(a) before and after dialytic treatment in patients on maintenance hemodialysis. They observed depressed protein C activity that significantly (p < 0.005) increased and became normal immediately after hemodialysis while factor X and factor VII increased (p < 0.01; p < 0.05) despite heparinization together with amount of serum lipoprotein(a). In vitro incubation (30' at 37 degrees C) of uremic and healthy blood showed a decrease in serum lipoprotein(a) concentration. After heparin addition (final concentration 0.5 U/ml) lipoprotein(a) increased in the uremic blood only. The clinical and physiopathological implications of these results are discussed.