To investigate whether the nutritional improvement achieved by recombinant human erythropoietin (rHuEPO) treatment is the result of anemia correction with rHuEPO or the direct anabolic effects of rHuEPO per se, nutritional assessment was performed in 2 studies (study I and II) on hemodialysis (HD) patients. Nutritional assessment included blood biochemistry determinations, anthropometric measurements, daily protein intake (DPI) and dialysis efficiency. In study I, 5 HD patients who had not been given rHuEPO and had a hematocrit (Hct) of < or = 25%, were administered rHuEPO at the initial dose of 96.2 U/kgBW. Nutritional assessment of these patients was performed before rHuEPO treatment and every 4 weeks until the 24th week after rHuEPO treatment. In study II, the same nutritional assessment as in study I except for DPI, was performed in 2 groups with the same Hct level and dialysis regimen; an EPO group (n = 8) previously given rHuEPO (88.2 +/- 13.7 U/kgBW, 25.8 +/- 2.5 mos) and a non-EPO group (n = 8) not given rHuEPO. In study I, the mean Hct level was significantly increased 4 weeks after rHuEPO treatment (23.3 +/- 0.6 to 26.9 +/- 0.9%). However, the nutritional parameters and dialysis efficiency were nearly constant over 24 weeks, suggesting either the absence of a short-term direct anabolic effect of rHuEPO or masking of such an effect due to general condition improvement by anemia correction with rHuEPO. In study II, no significant differences in nutritional assessment were confirmed between the groups, suggesting that a long-term direct anabolic effect of rHuEPO may not exist and nutritional improvement may result from correction of anemia with rHuEPO.(ABSTRACT TRUNCATED AT 250 WORDS)