We studied tissue plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1) levels in plasma and peritoneal effluent in 10 children on continuous ambulatory peritoneal dialysis (CAPD) before, and 8 and 12 weeks after, treatment with recombinant human erythropoietin (rHuEPO). Plasma t-PA and PAI-1 levels were lower in patients than in controls during the study. The plasma t-PA levels were increased by rHuEPO treatment. Although PAI-1 levels showed a tendency to increase in the early phase of rHuEPO treatment, they later returned to near baseline levels. Peritoneal effluent t-PA levels were decreased at week 8 of treatment, but returned to baseline levels at week 12. Peritoneal effluent PAI-1 levels were not changed by the rHuEPO treatment. No correlation was observed between levels of t-PA and PAI-1 in plasma and in peritoneal effluent. No correlation was seen between plasma PAI-1 levels and duration of CAPD. A significant negative correlation was found between the plasma PAI-1 levels and hemoglobin levels at week 8 and week 12. These results suggest that plasma t-PA levels can be increased by rHuEPO treatment, while plasma PAI-1 levels are associated with hemoglobin levels.