1. Muscle protein breakdown in vivo has been studied by measurements of urinary 3-methylhistidine/creatinine ratios. No differences were found between control subjects and chronic alcoholics either with or without proximal muscle wasting or cirrhosis.
2. Calculation of muscle turnover rates, with the correction of Afting et al. (1981, Biochemical Journal, 200, 449-452) for non-skeletal muscle contributions of 3-methylhistidine and creatinine, showed lower values for alcoholics compared with controls.
3. Tissue activities of a neutral protease, assayed by a novel, rapid and sensitive fluorimetric method, were similar in patients and controls. The activity did not vary with severity of atrophy or the presence of cirrhosis.
4. No evidence was therefore obtained to suggest that alcoholic myopathy is due to increased muscle breakdown.