1. Total renal blood flow and its cortical distribution were measured by the radioactive microsphere technique in conscious rabbits and after anaesthesia with pentobarbitone, chloralose-urethane or ether.
2. Pentobarbitone anaesthesia caused a fall of 26% in total renal blood flow, of 26% in superficial cortical flow, and of 24% in deep cortical flow. Sodium excretion rate fell by 33%.
3. Chloralose-urethane anaesthesia caused no change in total or regional renal blood flow, or in sodium excretion.
4. Ether anaesthesia caused an insignificant fall in total renal blood flow, but superficial cortical flow fell by 13 % and deep cortical flow rose by 21 %. Urinary sodium excretion fell by 65%.
5. Possible mechanisms for these changes in response to anaesthesia are discussed.
6. The effects of anaesthetic agents may influence the interpretation of published work on control mechanisms in the renal circulation.