Energy expenditure and substrate oxidation rate for fat, glucose and protein were evaluated by indirect calorimetry in 20 normal individuals, 35 patients with acute hepatitis and 22 patients with biopsy-proven alcoholic cirrhosis in the postabsorptive state. Measurements were done in the resting state after an overnight fast (10 to 12 hr). Oxygen consumption (ml/min/1.73 m2) in normal subjects, in patients with acute hepatitis and in patients with cirrhosis was 206.5 +/- 4.0 (mean +/- S.E.M.), 216.4 +/- 4.7 and 228.8 +/- 7.1 (p less than 0.05 vs. controls), respectively. When related to body surface area (kcal/min/1.73 m2), resting energy expenditure did not differ between normal subjects (0.98 +/- 0.02), patients with acute hepatitis (1.03 +/- 0.02) and cirrhotic patients (1.06 +/- 0.03). However, when related to 24-hr urinary creatinine excretion as an estimate of lean body mass, energy expenditure was increased in cirrhosis (p less than 0.0001). In cirrhosis an inverse association between the severity of liver disease according to Pugh and oxygen consumption and resting energy expenditure was found. In cirrhotic patients the percentages of total calories derived from fat (86% +/- 5%), carbohydrate (2% +/- 4%) and protein (12% +/- 1%) were different from those of normal controls who metabolized 45% +/- 4%, 38% +/- 4%, 17% +/- 1%, respectively. In acute hepatitis no alterations in metabolism could be found apart from a decreased protein oxidation rate. In conclusion no appreciable changes in energy metabolism exist in acute hepatitis. The pattern of fuel use in cirrhosis resembles that in starvation.(ABSTRACT TRUNCATED AT 250 WORDS)