The plasma concentration of immunoreactive human brain natriuretic peptide (ir-BNP) was measured in 40 patients on hemodialysis (HD) and in 12 healthy subjects. Immunoreactive human atrial natriuretic peptide (ir-ANP) was also measured. The mean (+/- SE) plasma ir-BNP concentration in the patients before HD (18.4 +/- 3.4 fmol/mL) was markedly higher than that in the control group (0.39 +/- 0.08 fmol/mL). The plasma ir-BNP level was significantly decreased by HD from 18.4 +/- 3.4 fmol/mL to 10.5 +/- 2.2 fmol/mL (P < 0.001), but the latter value was still higher than the upper limit of the normal range for our laboratory. There were significant correlations between the plasma ir-ANP level and the mean blood pressure before HD (P < 0.05) and between the HD-induced changes in plasma ir-ANP level and mean blood pressure (P < 0.001). These correlations were not observed between the plasma ir-BNP level and mean blood pressure. The plasma ir-BNP level correlated with the cardiothoracic ratio and this correlation was closer to that between the plasma ir-ANP level and cardiothoracic ratio. Ultrasound echocardiographic studies in 13 patients revealed that the pre-HD state of high cardiac output was correlated by HD in association with decreases in plasma ir-BNP and ir-ANP levels. Correlations were observed between the pre-HD ir-ANP level and the interventricular septal thickness index (r = 0.68, P < 0.05) and between the change in ir-BNP level and that in left atrial diameter (r = 0.806, P < 0.001). In conclusion, BNP levels were high in HD patients compared with the control subjects and were decreased during HD. In addition, BNP and ANP levels correlated with several parameters of volume change and cardiac status.