AJ'ter partial hepateetomy, ttle liver undergoes an array of metabolic changes until regeneration is complete. Since carbons derived from alanine can be ineorporated into most metabolic pools, we studied the metabolism of Z4C-labeled alanine during the early phase of regeneration. Sham operated (controls) and partially hepateetomized rats weighing about 200 g each were injected intraperitoneally with l-[U-z4C]alanine at 9, 18, and 36 hours after surgeo'. The animals were killed 2 hours after it(/ection. Compared to the controls, alanine oxidation was markedly depressed (P < 0.05) in the 9and 18-hour groups, but was restored in the 36-hour group. The specific activity of plasma glucose and hepatic glycogen was elevated 9 and 18 hours after partial hepatectomy. There was a corresponding increase in the activities of fructose-l,6-diphosphatase and phosphoenolpyruvate carboxykinase. Hepatic protein specific activity increased by 30, 74, and 120%, respectively 9, 18, and 36 hours after partial hepatectomy. Hepatic Jatty acids followed a similar pattern. In a separate set of experiments, the distribution of radioactivity in glutamic acid was measured. The results showed that alanine carbons enter the citric acid cycle primarily via the acetyl CoA pathway in the controls, bat via the oxaloacetate pathway in partially hepateetomi=ed rats. The results demonstrate significant changes in the activities of metabolic pathways qfalanine in the early phase of hepatic regeneration.