Renal blood flow and hemodynamic autoregulation were assessed in seven chronically instrumented canines studied in the conscious state and after pentobarbital anesthesia administration (30 mg/kg). The effects of acute arterial hemorrhage (10 and 15 ml/kg) were also studied. In the conscious state, no significant changes in autoregulation were observed following 10 mg/kg hemorrhage. With pentobarbital and 10 ml/kg hemorrhage, a significant change in the limits of autoregulation was noted (autoregulatory limit 78.5 +/- 16.6 vs. 88.4 +/- 25.3 mmHg, P less than 0.05). Four animals were also studied in the conscious state following 15 ml/kg acute arterial hemorrhage. In these animals, mean arterial pressure decreased (from 105.0 +/- 11.4 to 87.8 +/- 7.2 mmHg, P less than 0.025) but renal blood flow (from 293 +/- 38 to 272 +/- 65 ml/min) and autoregulatory limit did not change. We conclude that renal blood flow is unaffected by hemorrhage or pentobarbital alone. In the conscious state, renal pressure-flow autoregulation is maintained despite moderate hemorrhage and systemic hypotension. The lower limit of autoregulation is significantly changed by even minor hemorrhage in the pentobarbital-anesthetized state.