Very few patients with chronic renal failure (CRF) can maintain a hemoglobin concentration > 12 g/dl without rHuEpo treatment. Among 68 patients treated in our Department by CAPD, 12 of them (17.6%) with daily diuresis < 400 ml, for at least 6 months had Hb level over 12 g/dl, Hct > 35% without rHuEpo treatment. In present study we carried out a clinical analysis of 12 patients without anaemia treated CAPD from 12 to 63 months. Mean Hb value was 13.5 +/- 0.97 g/dl (range 12.4-14.9 g/dl). None of 12 patients had acquired cystic kidney disease in ultrasonographic investigation. Nobody of these patients was rHuEpo treated. Mean C-reactive protein as well as ferritin serum concentrations was significantly lower in this group of patients compared to others. Mean endogenous Epo concentration was not significantly different from other CAPD pts. We conclude that spontaneous increase in Hb concentration in CAPD pts was not connected with increase in the serum endogenous Epo concentration. Factors other than Epo probably play a role in regulation of erythropoiesis in these pts.