The influence of total parenteral nutrition (TPN) on whole-body energy metabolism and nitrogen balance in relation to the activities of key enzymes, the flux of glucose-carbons, RNA content and protein synthesis in skeletal muscles was evaluated in a study of depleted cancer and non-cancer patients. TPN consisted of D-glucose, lipids and amino acids as 47.8 kJ/g N (200 kcal/gN); 30 per cent of the non-protein energy was glucose and 70 per cent was lipids during 14.9 +/- 1.3 d (mean +/- s.e.). Body weight and body potassium increased during TPN. Positive whole-body energy and nitrogen balance were achieved and associated with improved translational capacity for protein synthesis in skeletal muscle (m. rectus abdominis) in vitro. Increased RNA content of muscle after TPN showed that transcriptional events were involved in vivo. The initial low levels of activities (Vmax) of glycolytic and oxidative key enzymes in skeletal muscle were not significantly changed by the 2-week period of TPN.