Severe hemorrhage in pentobarbital-anesthetized dogs (25 mg/kg) is reversed by intravenous NaCl (4 ml/kg, 2,400 mosmol/l, 98% long-term survival). This paper compares survival rates and hemodynamic and metabolic effects of hypertonic NaCl with sodium salts (acetate, bicarbonate, and nitrate), chlorides [lithium and tris(hydroxymethyl)aminomethane (Tris)], and nonelectrolytes (glucose, mannitol, and urea) after severe hemorrhage (44.5 +/- 2.3 ml/kg blood loss). Sodium salts had higher survival rates (chloride, 100%; acetate, 72%; bicarbonate, 61%; nitrate, 55%) with normal stable arterial pressure after chloride and nitrate; near normal cardiac output after sodium chloride; normal acid-base equilibrium after all sodium salts; and normal mean circulatory filling pressure after chloride, acetate, and bicarbonate. Chlorides and nonelectrolytes produced low survival rates (glucose and lithium, 5%; mannitol, 11%; Tris, 22%; urea, 33%) with low cardiac output, low mean circulatory filling pressure, and severe metabolic acidosis. Plasma sodium, plasma bicarbonate, mean circulatory filling pressure, cardiac output, and arterial pressure correlated significantly with survival; other parameters, including plasma volume expansion or plasma osmolarity, did not. It is proposed that high plasma sodium is essential for survival.