Hyperprolactinemia is known to cause impotence in patients with normal renal function and elevated serum prolactin levels (SPLs) have also been reported in uremia. This study was undertaken to examine a possible role of elevated SPLs in the impotence of male patients undergoing chronic hemodialysis (CHD). SPLs in 16 male patients undergoing CHD were evaluated using a homologous double-antibody radioimmunoassay with prolactin isohormones isolated from human amniotic fluid. Patients were divided in 2 groups: 6 patients were sexually impotent and 10 sexually potent. Patients with emotional disturbances or marital conflicts known to cause impotence were excluded from the study. The SPLs of the impotent patients were found to be significantly elevated in comparison to the levels of the potent patients (136.7 ± 28.2 vs. 37.3 ± 2.7 ng/ml, p < 0.001). Furthermore, in 2 patients who were sucessfully treated with bromocriptine to suppress hyperprolactinemia, recovery of sexual potency was noted. Thus, sexual impotence in male CHD patients seems to be associated with marked hyperprolactinemia. It is suggested that elevated SPLs may be an important cause of impotence among CHD patients.