Effect of beta-adrenoceptor blockade on the changes in rectal temperature (RT), heat production (HP) and noradrenaline (NA) concentration in the submaxillary salivary glands (SMSG) of rats exposed to heat (45 degrees C) was studied. Propranolol (P) (15 mg/kg i.p.) decreased the tolerance to heat. The survival time of propranolol-treated (PT) rats was 30 min shorter. The temperature curve of control rats exposed to heat can be divided into three phases: a rapid rise in RT; a plateau (TP) and a prelethal increase. In PT animals, under identical conditions, TP disappears and RT further rises accelerating death. In the initial phase of heat exposure, HP was markedly decreased to the same extent in both experimental groups; but after 20 min HP increases in PT rats. The content of NA from SMSG both in the initial phase and in the TP phase is modified in PT rats.