Plasma levels of atrial natriuretic peptide (ANP), renin activity (PRA), and endothelin (ET) are often elevated in uremic patients on hemodialysis treatment. The profile of these vasoactive hormones and their relationships with hemodynamic indices in patients on continuous ambulatory peritoneal dialysis (CAPD), however, are not clear. We therefore measured plasma concentrations of ANP, PRA, ET, together with parathyroid hormone (PTH) in 17 patients (mean age 38.5 years) on maintenance CAPD over a period of 12 weeks. Baseline ANP, PRA, and ET levels were significantly higher than those of healthy subjects, and no significant changes in these indices were observed over the 12 week period. There was a significant positive correlation between levels of plasma ANP and PRA [rank correlation coefficient, R(s) = 0.496, p less than 0.05] as has been reported in cardiac failure. Despite the absence of clinically overt heart failure, a significant proportion (approximately 50%) of our patients demonstrated evidence of myocardial dysfunction on echocardiography. Furthermore, a significant positive correlation was demonstrated between plasma ANP and left atrial size [R(s) = 0.61, p less than 0.01] and an inverse correlation existed between plasma ANP and the left ventricular ejection fraction [R(s) = 0.51, p less than 0.05]. Twelve patients (71%) had biochemical evidence of hyperparathyroidism with raised levels of serum PTH. Our study demonstrates increased levels of plasma ANP, PRA, and ET in uremic patients on long-term CAPD. A positive correlation exists between plasma ANP and PRA suggesting their myocardial function may be compromised and this was confirmed on echocardiography. The possibility that high circulating PTH concentrations contribute to impaired cardiac function in such patients, deserves further study.