Mitochondrial encephalomyopathy is a genetic disorder for which there is at present no cure. Conventional treatment regimes may not be effective in preventing weight loss and muscle wasting in many patients. Recombinant human GH has been shown to have anabolic effects on protein metabolism and to reduce muscle wasting in various diseases. We have treated a patient known to have myoclonus, epilepsy with ragged red fibres (MERRF) with a high protein diet for 1 month followed by a high protein diet and GH therapy for 1 month. To assess the benefit of these treatments the patient underwent whole body protein turnover, myometric and body composition studies at baseline, following the high protein diet (100 g/day) and following GH therapy. Whole body protein synthesis (and protein breakdown) increased following a high protein intake and was further enhanced by treatment with GH and in a high protein diet. Body composition did not change significantly following treatment with either the high protein diet or GH but there was an improvement in muscle performance following GH treatment. Mitochondrial encephalomyopathy, a wasting disorder, may be a disease in which the known protein anabolic effect of GH may have a therapeutic benefit.