The high plasma levels of the vasodilating hormone atrial natriuretic peptide (α-ANP), observed in patients with chronic renal failure, decrease substantially during hemodialysis (HD), probably owing to volume reduction. Cardiovascular stability is better maintained by the use of cold dialysate although underlying mechanisms are unknown. In order to investigate the effects of different dialysate temperatures on hemodynamic stability and plasma levels of immunoreactive ANP (p-irANP), 10 stable HD patients were dialyzed with bicarbonate dialysis fluid for 240 min with each of 3 different dialysate temperatures: 36.5 °C (normal HD; NHD), 38.5°C (warm HD; WHD) and 34.5°C (cold HD; CHD). A Cuprophan plate dialyzer was used. The ultrafiltration volume and ultrafiltration rate were identical in each patient during the treatments. p-irANP was determined by radioimmunoassay, using 2 antisera which different cross-reactivity to ANP-related peptides. During NHD a nonsignificant decrease in mean arterial blood pressure from 111 ± 5 to 103 ± 8 mm Hg was observed. A significant (p < 0.05) decrease in mean arterial blood pressure from 109 ± 4 to 96 ± 6 mm Hg occurred during WHD, while during CHD it remained stable (111 ± 4 before, 112 ± 5mm Hg after). Irrespective of the dialysate temperature or the antiserum used, p-irANP decreased significantly (p < 0.05) during the treatment. The reduction in p-irANP was delayed during CHD, the decrease being significantly (p < 0.05) less pronounced after 120 min. At the end of the treatment no significant difference was observed between the regimes. In conclusion, together with the improvement of hemodynamic stability during CHD a delayed decrease in p-irANP was observed. Thus, α-ANP does not seem to be primarily involved in the stabilization of blood pressure duri