Effects of footshocks (FS) on antidiuretic hormone (vasopressin, VP) in the plasma were studied in rats. Continuously applied FS of 60s period with 5ms pulses at 50Hz frequency significantly increased VP as well as adrenocorticotrophic hormone (ACTH) in the plasma in a time- and shock intensity-dependent manner. Contrarily, the 50Hz FS of 2s period as repeated intermittently at every 15s for over the period of 2, 10, and 30min were much less effective for increasing plasma VP, whereas these intermittent FS increased plasma ACTH to an extremely high level. During the inter-shock intervals of 13s between successive two shock periods rats exhibited a "freezing" behavior. Hypertonic saline or urethane injected I.P, immediately after termination of the intermittent FS significantly increased VP as well as ACTH in the plasma. These data clearly indicate that FS potentiate VP secretion and suggest the possibility that emotional stress may suppress the noxious stimuli-induced VP secretion.