The acute modifications of atrial natriuretic peptide (ANP) plasma levels due to intraperitoneal dialysate infusion and the relationship between ANP and arterial blood pressure were studied in 17 patients on continuous ambulatory peritoneal dialysis (CAPD). ANP plasma levels were 159.18 +/- 87.06 pg/ml 30' minutes after 2.000 ml of peritoneal dialysate filling (t = 2.55; p less than 0.02). There was no correlation between ANP and arterial blood pressure neither before (r = -0.10; p = n.s.), nor after intraperitoneal dialysate infusion (r = 0.05; p = n.s.).