Renal ischemia was produced in anesthetized rats by a bilateral ligation of the renal artery, vein, and ureter. Pretreatment with hydralazine (0.3-10.0 mg/kg i.v.) resulted in a dose dependent reduction in elevated plasma creatinine levels 24 hr after a 60 min ischemic episode, indicating a protective effect on post-ischemic renal function. Hydralazine (3.0 mg/kg, i.v.) produced a fall in arterial blood pressure and exaggerated and/or extended post-ischemic depressions in renal blood flow, renal transport activity (in vitro para-aminohippurate uptake) and renal ATP levels. These results indicate that the hypotensive activity of hydralazine may have indirectly benefited the post-ischemic kidney by prolonging a relative anoxic condition which possibly allowed renal cells to recover under conditions where minimal tubular activity was present.