Isoproterenol-induced thirst in rats has been attributed to the activation of beta-adrenergic receptors. Since these receptors can be further differentiated pharmacologically into beta1 and beta2 types, experiments were performed using several beta-adrenergic agonists and antagonists to determine the receptor type initiating the isoproterenol-induced thirst. The beta1- and beta2-adrenergic antagonist, d,l-propranolol (1 mg/kg, ip), blocked the increase in water intake usually accompanying acute subcutaneous administration of isoproterenol (25 microgram/kg) to female rats. Since l-propranolol is known to stabilize membranes and to possess anesthetic-like properties, d-propranolol was also used. This isomer has little beta-adrenergic-blocking activity but possesses anesthetic-like activity. Administration of d-propranolol (1 mg/kg, ip) failed to affect the drinking response to acute administration of isoproterenol (25 microgram/kg). Practolol (125 mg/kg), a beta1-adrenergic antagonist with little anesthetic properties, also had no effect on water intake of isoproterenol-treated rats. Butoxamine, a selective beta2-adrenergic antagonist, attenuated the drinking response to isoproterenol. Salbutamol (150 microgram/kg), a beta2-adrenergic agonist, mimicked the effect of isoproterenol on water intake. These results are consistent with the suggestion that beta2-adrenergic receptors mediate the isoproterenol-induced thirst in rats.