Effects of a dopamine D1 receptor antagonist, SCH 23390, were investigated on plasma level of vasopressin after stressful stimuli in rats. The antagonist markedly attenuated the increase in plasma level of vasopressin after electric footshocks but not after s.c. injected hypertonic saline. The antagonist, however, did not significantly change the suppressive vasopressin response to fear-related emotional stress, though the drug suppressed motor behavior of the rat during testing period. These data suggest that dopamine D1 receptors play an important role selectively in the facilitatory vasopressin response to noxious stimuli in rats.