Studies of renal autoregulation in pancreatectomized and streptozotocin diabetic rats. We studied renal autoregulation in pancreatectomized Munich-Wistar diabetic rats and in their sham-operated controls. In a second experiment we studied renal autoregulation in untreated and insulin treated streptozotocin diabetic Munich-Wistar rats and their nondiabetic controls. In the first experiment the diabetic rats had higher baseline renal blood flows (RBF). There was a fall in renal vascular resistance (RVR) and sustained RBF in both diabetic and control rats as renal perfusion pressures (RPP) was reduced from 130 and 110 mm Hg. As RPP was reduced from 110 and 80 mm Hg, there was no significant change in RVR in control rats and RBF began to fall. Below RPP of 80 mm Hg RVR rose and RBF fell sharply in these rats. In contrast, there was a progressive fall in RVR as RPP was lowered to 60 mm Hg in the diabetic rats and, thus, RBF was much better sustained in these animals. In the second experiment the plasma glucose level was 502 ± 52 mg/dl (X̄ ± SD) in the untreated diabetic rats and only modestly reduced to 411 ± 49 mg/dl in the insulin treated animals. Untreated streptozotocin diabetic rats had moderately reduced and insulin-treated diabetic rats had mildly reduced baseline RVR and RBF. However, in these animals as in the pancreatectomized rats the increases in RVR noted in control rats at subautoregulatory RPPs were not seen. Thus, regardless of whether baseline RBFs were increased or decreased, diabetic rats sustained RBF at markedly reduced RPPs far more efficiently than did nondiabetic rats. The pathogenesis of these abnormalities in diabetic rats was not learned in these studies. However, it is likely that further study of autoregulation in diabetic rats could uncover factors influencing renal vascular tone which would be helpful in understanding the renal hemodynamic perturbations which may attend this experimental model.