The relationship among parenteral nutrition, hepatic energy charge, and mitotic activity was investigated in partially hepatectomized rats fed diets based on glucose, ketone bodies, and saline (starvation). Male Sprague-Dawley rats underwent 70% hepatectomy and jugular vein catheterization for parenteral feeding. All rats were infused with saline for 6 hours, then randomly assigned to one of three parenteral infusions. Rats received either 0.9% saline only (group A rats), 25% glucose + 4% amino acid (group B rats), or 18% monoacetoacetin + 7% glucose + 4% amino acid (group C rats). Three rats receiving saline infusion were killed at 2, 4, and 6 hours after surgery, and three rats from each diet group were killed at 2- to 4-hour intervals from 10 through 32 hours. Hepatic energy charge and mitotic index were measured at each time point. Energy charge was similar for each treatment until 18 hours but was depressed from 6 through 16 hours and began to increase between 16 and 18 hours. Energy charge at 22 hours for group B rats was significantly higher than energy charge for group A and C rats. This difference was maintained through 32 hours. Mitosis started between 24 and 26 hours for all treatments, and group A and C rats exhibited a much higher mitotic index than did group B rats. Adenosine triphosphate was the main driving force for changes in energy charge. The data showed that energy charge and mitotic index were inversely related. It is speculated that high energy charge may negatively influence activity of enzymes inasmuch as activity of these enzymes is altered by phosphorylation-dephosphorylation.