To clarify the mechanism of high susceptibility to infection in cirrhotics, the changes in adenylate energy charge and MTT assay in peripheral blood lymphocytes were studied in cirrhotic and noncirrhotic patients in the early postoperative period after hepatectomy. The adenylate energy charge measured by radioactive labeling of the lymphocyte adenine nucleotide pool showed no significant difference preoperatively between cirrhotics and noncirrhotics, but a significant difference was observed in the pre- and postoperative distribution of adenine nucleotide metabolites ( P < 0.01). In the cirrhotic group, the adenylate energy charge of lymphocytes decreased significantly to 0.807 ± 0.011 on the third postoperative day compared with preoperative value (0.891 ± 0.006, P < 0.01) and was restored to the normal range on the fifth and tenth postoperative days (0.886 ± 0.006, 0.899 ± 0.014), while no significant decrease was observed in the noncirrhotic group. MTT assay revealed that lymphocyte cell function decreased significantly in cirrhotics after hepatectomy. These results indicate that, in cirrhotic patients, the energy metabolism of lymphocytes is already impaired to some extent preoperatively, and that it undergoes further deterioration when surgical stress is applied. It is suggested that the decreased energy metabolism in the lymphocyte may be responsible for the increased susceptibility to infection in postoperative cirrhotics.