The plasma concentration of human brain natriuretic peptide (BNP) was measured by immunoradiometric assay in patients on maintenance hemodialysis (HD) to assess the possible relationship between the plasma levels of this peptide and cardiac ventricular function, as judged by M-mode echocardiography. The plasma BNP levels in the pre-HD state were significantly higher (688.5 ± 154.5 pg/ml) than those of healthy subjects (<40 pg/ml). In addition, the plasma BNP levels were slightly decreased during HD (post-HD, 617.3 ± 157.1 pg/ml). There was no correlation between the plasma levels of BNP and body weight changes during HD. The mean plasma BNP level was significantly higher in the group of patients with a low left ventricular ejection fraction (EF < 60%) than in the group with a normal EF. In the patients as a whole, there was an inverse correlation between plasma BNP levels and EF. Moreover, a positive correlation was found between plasma BNP levels and left ventricular mass index (r = 0.57, p < 0.05). These results suggest that plasma BNP levels increase in response to chronic stimulation in accordance with increased cardiac load, and that they may be a possible indicator of reduced ventricular function in HD patients.