1. Dogs cooled to 27°C were compared with control dogs maintained at 38°C. The mean arterial blood pressure, renal blood flow and glomerular filtration rate were lower in the hypothermic animals.
2. The relation between mean arterial blood pressure and renal blood flow was investigated. Autoregulation of renal blood flow occurred in the kidneys of normothermic and hypothermic animals. Thus the reduction in renal blood flow during hypothermia is not due simply to the fall in mean arterial blood pressure.
3. Similarities between recordings of renal blood flow obtained at 38°C and 27°C suggest that its autoregulation occurs by the same mechanism at the two temperatures.
4. Autoregulation of renal blood flow occurred in hypothermic kidneys in the presence of a cold-induced vasoconstriction. The observed responses to cold and to alterations in mean arterial blood pressure may take place in different areas of the renal vasculature.