1. The aim of this study was to elucidate the role of atrial natriuretic peptides in the regulation of water and electrolyte balance after alcohol intake. To this end we measured the plasma concentrations of ethanol, atrial natriuretic peptide 99-126 and the N-terminal fragment of pro-atrial natriuretic peptide (atrial natriuretic peptide 1-98), serum osmolality and serum sodium concentration, and urine output, urine osmolality and urinary sodium excretion for 12 h after administration of ethanol (0, 0.5 and 1.0 g body weight/kg) and placebo drinks to nine healthy subjects according to a double-blind cross-over design. 2. Intake of ethanol (at 19.00-19.45 hours) inhibited the nocturnal increase in the plasma atrial natriuretic peptide 99-126 level dose-dependently (P < 0.05), but had no effect on the plasma atrial natriuretic peptide 1-98 level. Serum osmolality and serum sodium concentration were elevated dose-dependently for 2-5 h after the ethanol intake. Urine volume increased after the higher ethanol dose (net loss of 0.6 litre of water). 3. Since the plasma atrial natriuretic peptide 1-98 level was not changed after ethanol intake, we propose that the alcohol-induced inhibition of the nocturnal rise in the plasma atrial natriuretic peptide 99-126 level is not caused by an inhibition of release, but may rather reflect an increased peripheral elimination of atrial natriuretic peptide 99-126.