1. The rate of efflux of ketone bodies has been studied in isolated hepatocytes prepared from starved rats and preloaded with d-3-[14C]hydroxybutyrate.
2. Efflux of ketone bodies was temperature-dependent, saturable and inhibited by α-cyano-3-hydroxycinnamate and phloretin. The rate of efflux was also reduced by 6 mmol/l lactate and pyruvate added to the external medium.
3. Under conditions of simulated metabolic acidosis in the hepatocyte suspension medium, ketone body efflux rate was reduced.
4. The experimental data suggest that hepatic plasma membrane ketone body transit is carrier-mediated.