IT has recently been observed that patients with Duchenne muscular dystrophy (DMD) have a significant defect in the uptake of serotonin (5-HT) into platelets¹, raising the possibility that a defect in the metabolism of biogenic amines may be important in the pathogenesis of the skeletal muscle lesions of this disorder. If monoamines such as 5-HT or norepinephrine (NE) which are dependent on the intracellular enzyme, monoamine oxidase (MAO), have a diminished ability to reach this site of metabolism, increased tissue levels of these compounds could result and produce skeletal muscle damage. The effect of such a defect would be enhanced in skeletal muscle as catechol-O-methyltransferase, the alternative pathway for metabolism of biogenic amines, is absent from this tissue². Support for this hypothesis of skeletal muscle damage is found in the observation that skeletal muscle from biopsies of Duchenne dystrophy patients has shown the presence of an abnormal intrafibrillar fluorescence (Falck-Hillarp technique) presumed to be a monoamine-like substance³. Furthermore, injection of the MAO inhibitor, pargyline, results in a myopathy with evidence for accumulation of monoamines⁴. The pargyline induced myopathy, however, has serious limitations as a model for Duchenne dystrophy, as the lesions are limited to the soleus muscle and, furthermore, MAO activity has been found to be normal in patients with DMD (ref. 1).