In order to investigate nutritional status in relation to the metabolic state of skeletal muscle in patients with severe congestive heart failure, and to explore the influence of long-term dietary supplementation, 22 patients were randomized in a double-blind study to receive either a placebo (n = 13) or high caloric fluid (n = 9). Before treatment, the muscle content of adenosine triphosphate (ATP), creatine and glycogen was lower than in healthy individuals, and muscle biopsies revealed an excess of water. Two patients were found to be malnourished according to nutritional assessment criteria. Following study treatment, no significant changes occurred, either within or between the two subgroups. Thus, patients with severe congestive heart failure displayed metabolic derangement in skeletal muscle which did not seem to be explained by malnutrition.