We have previously reported the association of significant malnutrition with pulmonary emphysema and noted that the degree of malnutrition correlated with some measures of pulmonary function. The purpose of this study was to examine the energy requirements of malnourished patients with emphysema and acute effects of nutritional repletion on indices of pulmonary function and nutrition. We studied 6 malnourished patients with emphysema during a 3-wk admission to a clinical research unit. Initially, patients were allowed access to standard food sources ad libitum. Subsequently, if caloric goals were not met, nutritional supplementation was given orally. All patients receiving the ad libitum diet ingested calories in excess of their maintenance energy requirements. All patients increased their body weight (p less than 0.001) and percent ideal body weight (p less than 0.001). Anthropometric nutritional parameters showed a small but significant improvement (p less than 0.05). Although there was no significant change in spirometric results, lung volumes or DLCO after 3 wk maximal inspiratory mouth and transdiaphragmatic pressures increased (p less than 0.005). Peripheral skeletal muscle strength as measured by handgrip also improved (p less than 0.001). We conclude that inability to ingest an adequate number of calories was not the cause of weight loss in these patients. We also found that when given sufficient calories in excess of their needs, patients gain weight. Weight gain and improvement in anthropometric measurements are accompanied by significant improvement in ventilatory and peripheral muscle strength.