The effects of intravenous arginine-vasopressin (AVP) on the endocochlear potential (EP) and systemic blood pressure (BP) were examined in the guinea pig. Intravenous AVP (10(-7) M) elevated BP significantly but did not change EP. AVP (10(-8) M) produced a significant decrease in the amplitude of EP but did not change mean blood pressure significantly. AVP at 10(-9) M did not affect EP or BP. These results suggest that intravenous AVP might have an inhibitory effect on EP.