To determine whether the renal sympatho-inhibition and bradycardia in responses to acute increases in arterial pressure are altered in the diabetic state, the renal nerve discharge and heart rate were measured in streptozotocin (STZ) induced diabetic (DIA) rats. Integrated renal sympathetic nerve activity and heart rate were measured before and during an acute increase in blood pressure in anesthetized (Inactin 0.1 g/kg, i.p.) control (vehicle) and DIA rats (Sprague Dawley rats injected with STZ 65 mg/kg i.p.). Blood glucose levels were significantly elevated in the DIA group compared with the control group. Baroreflex changes in renal nerve activity and heart rate were not significantly different in the DIA rats compared with control rats at a time when the renal sympatho-inhibition in response to acute volume expansion was blunted in the diabetic rats. In addition, blocking the effect of elevated angiotensin II in diabetic rats with the converting enzyme inhibitor enalapril did not change the baroreflex function in DIA rats compared with control rats. However, administration of vasopressin failed to potentiate the baroreflex in diabetic rats as it did in normal control rats. This study demonstrates that (1) the baroreflex function is normal in STZ induced diabetic rats unlike the volume reflex during the early phase of the disease, (2) blockade of the AII system does not alter baroreflex function in diabetic rats and (3) vasopressin fails to potentiate the baroreflex in diabetic rats as it does in the euglycemic normal rats.