1. Ammonium acetate (13 mmol) was injected intravenously over 10 min into fourteen dogs. This consistently caused a transient depression in both cerebral and limb oxygen consumption.
2. An equivalent dose of ammonium chloride given to five dogs caused a similar decrease but ammonium hydroxide caused a slight increase.
3. The decreased cerebral oxygen consumption and blood flow caused by ammonium acetate infusion was abolished by simultaneous intravenous administration of sodium bicarbonate (five dogs). Sodium chloride did not abolish it. Bicarbonate alone did not alter oxygen consumption or blood flow.