Acute exposure of male rats to cold (5.degree. C) leads to a rapid increase of plasma levels of thyrotropin (TSH), prolactin (PRL), corticosterone and L-thyroxine. Exposure to ether is similarly followed by a rapid increase of plasma levels of PRL and corticosterone, while TSH release is inhibited. Acute treatment with dexamethasone (500 .mu.g) inhibits almost completely the PRL responses to both exposure to cold and ether stress, while the plasma TSH response to cold is only delayed and the decrease of plasma TSH observed after ether stress is unchanged. Basal plasma levels of both TSH and PRL are lowered after treatment with the steroid. Thyroxine treatment lowers the plasma TSH concentration to undetectable levels without affecting the plasma PRL response to cold or ether exposure. The rise of plasma PRL observed after cold exposure is probably not related to TRH, and common mechanisms may control ACTH and PRL secretion during acute stress exposure.