A prospective study of the evolution of serum erythropoietin level after androgen therapy was carried out in a group of 25 male patients on chronic hemodialysis treatment with nonferropenic anemia (serum ferritin > 50 ng/ml). The androgen used was nandrolone decanoate (200 mg/week intramuscularly, for 6 months). There was an increase of serum erythropoietin, that reached statistical significance in the 2nd week of treatment (8.6 +/- 6.4 vs. 14.2 +/- 9.8 mIU/ml, p < 0.05), and a stabilization after 1 month (1 month: 17.8 +/- 11.2 mIU/ml, 6 months: 19.6 +/- 14.9 mIU/ml). The hemoglobin also experienced a parallel increase to that observed in serum erythropoietin (basal value: 8 +/- 0.9 g/dl; at 1 month postandrogen: 9.2 +/- 1.3 g/dl, p < 0.001; at 6 months: 10.7 +/- 1.8 g/dl, p < 0.001). According to their response of serum erythropoietin the patients were divided into responders (15 patients) and nonresponders (10 patients). There were no differences between them concerning age, basal levels of serum erythropoietin and hemoglobin, and dose of nandrolone decanoate in relation to body weight. The evolution of hemoglobin was similar in both groups, and a correlation between serum erythropoietin and hemoglobin was not observed in the responder group. Fourteen patients were studied after androgen was discontinued. The serum erythropoietin returned to basal levels 6 weeks after the last dose of nandrolone decanoate (7.7 +/- 5.4 mIU/ml). However, hemoglobin was above the basal levels 16 weeks after discontinuing androgen (9.5 +/- 1.1 g/dl, p < 0.05), with no differences between the responder and nonresponder group.(ABSTRACT TRUNCATED AT 250 WORDS)