Volatile free fatty acids (VFA) in blood increased approximately twofold in dogs subjected to total hepatectomy. The average total plasma VFA preoperatively was 1,585 mug percent and shortly before death, postoperatively, was 2,798 mug percent. The corresponding red cell concentrations were essentially the same. Acetic acid was 81 percent of the total VFA, propionic acid 7 percent, isobutyric acid 4 percent, butyric acid one percent, and isovaleric acid 5 percent. There was little or no isovalerate in red cells. The increments in the individual fatty acids after hepatectomy were highly variable, but the average increase with time was almost linear. The increase in VFA probably reflects an increased utilization of the branched-chain aminoacids by extrahepatic tissues.