Controversy has existed over apparent dissimilarities in the autoregulatory capacities of the rat and dog. A protocol was designed to evaluate both the effects of the anesthetic agents. Nembutal (used most commonly in dogs) and Inactin (most frequently employed in rats) and the species peculiarities of these two mammals on autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). With Nembutal autoregulation of RBF was present in both experimental animals. Inactin impaired RBF autoregulation similarly in both species. With impaired RBF autoregulation similarly in both species. With either anesthetic GFR was autoregulated well in both rat and dog. Comparison of the two species revealed a greater RBF per gram kidney weight and a higher renal perfusion pressure (RPP) at which autoregulation of both hemodynamic parameters was lost in the rat. It is concluded from these studies that 1) the frequent use of Inactin in the rat in large part accounts for the observed lack of autoregulation of RBF in this animal and 2) renal hemodynamic responses are qualitatively similar in rat and dog when the same anesthetic agents are used.