The muscle contents of water, electrolytes, creatine, alkali-soluble protein (ASP) and carnitine were determined using percutaneous muscle biopsy technique. Seven patients with prolonged catabolic states and subsequent respiratory failure were studied. Twelve age- and sex-matched healthy subjects were used for comparison. The muscle content of alkali-soluble protein in relation to the content of DNA was less than half of control values, indicating a loss of more than 50% of muscle protein content. The muscle carnitine content was 25.9 +/- 6.5 mumol/g alkali-soluble protein, suggesting a preserved muscle carnitine concentration. Total muscle water was increased by over 20%, mainly due to an increase in extracellular water. Muscle sodium and chloride contents were doubled. The content of magnesium was slightly reduced but muscle potassium was normal. The marked depletion of muscle protein may have contributed to the requirements for artificial ventilation and the difficulties in weaning off the ventilator. The increase in muscle water masks the loss of metabolically active muscle tissue yielding low values for energy expenditure when relating to body weight. The benefit of the use of the ASP/DNA ratio in nutritional assessment is emphasised.