The influence of hepatitis B (HBV) and hepatitis C virus (HCV) infection on blood hemoglobin (Hb) and serum erythropoietin (Epo) and interleukin-6 (IL-6) concentrations was studied in 48 anemic patients on regular hemodialysis. They were grouped as follows: (I) 19 patients whose Hb values improved after infection (Hb > 85 g/L), (II) 10 patients with persisting anemia after infection (Hb < 75 g/L), and, without hepatitis virus markers (III) 8 patients with Hb > 85 g/L and (IV) 11 patients with Hb < 75 g/L. Serum immunoreactive Epo levels were significantly higher in group I (34.4+/-47.1 U/L) than in the other groups (II, 10.8+/-6.0; III, 7.9+/-3.2; IV, 8.4+/-4.3). Serum IL-6 was higher in group I than group III (7.7+/-7.8 pg/ml vs. 3.6+/-2.4; p = 0.05) but similar to the other groups. Hb levels in group I were maximal at the time of serum alanine aminotransferase normalization. Red cell production increases as a result of elevated circulating Epo during hepatic regeneration after HBV or HCV infection.