The effects of single ethanol doses on fluid and electrolyte metabolism were studied in 31 male mongrel dogs. The animals were given either 0.75 g/kg 1.50 g/kg, or 2.25 g/kg of a 25% (v/v) ethanol solution or isovolumetric quantities of water. Fluid intake, urine output, and electrolyte (Na, K, Cl, Mg) excretions were measured at 0--3, 3--8, and 8--24 hr. During the ascending portion of the plasma ethanol curve (0--3 hr) there was a diuresis and renal magnesium loss in the two highest dosage ethanol groups. During the initial portion of the descending plasma ethanol curve (3--8 hr), each ethanol group had a significant elevation in voluntary intake. At 8--24 hr, renal retention of sodium, potassium, and chloride was found in the 1.5 and 2.25 g/kg groups, and magnesium excretion was also reduced in the 2.25 g/kg group. Over the 0--24 hr, none of the ethanol groups showed fluid loss, while the 2.25 g/kg ethanol group had significant retention of water. The administration of the 2.25 g/kg ethanol dose also resulted in 24-hr retention of sodium and potassium.