Indirect calorimetry and nitrogen measurements suggest that uncomplicated abdominal surgery produces no significnat change in resting metabolic expenditure and only a slight loss of urinary nitrogen. More severe injury and infections produce larger increases in resting metabolic expenditure and nitrogen loss. Severe injuries can result in a 15 to 30% loss of body weight, but the protein contribution to caloric expenditure does not exceed 20% and is less than expected. The provision of calories and nitrogen can change the course of the septic patient. A continual conversion of alanine carbon to glucose occurs in septic patients, including those who are receiving exogenous glucose at the normal hepatic production rate. In sepsis, the release of glucogenic substrates from peripheral tissues may determine the rate of hepatic gluconeogenesis.