Most of the birds respond to angiotensin II (ANG II) (ip, 1-10μg/100g) by drinking. The receptive sites for ANG II are the preoptic area and the subfornical organ in the brain. However, species originating in arid areas and carnivorous birds, which drink little water in nature, are relatively insensitive to ANG II. It seems that ANG II has become adaptively involved in the physiological mechanisms inducing thirst during the evolutionary process. Among various other neuropeptides some have stimulatory and others inhibitory or no effects on water intake. Receptive sites for the active neuropeptides are located centrally, peripherally or in the kidney. However, it is not known whether the action is physiological in nature or not.