Nitric oxide is formed in skeletal muscle by the neuronal type nitric oxide synthase and the signalling function of dystrophin and related compounds are in part mediated by nitric oxide. Duchenne muscular dystrophy, mdx mice and patients with Becker dystrophy demonstrated neuronal type nitric oxide synthase deficiency in muscle biopsy specimens. We have intended to find out whether the plasma nitric oxide levels show any abnormality in patients with Duchenne muscular dystrophy. Serum NO levels of Duchenne patients (4.191 +/- 2.82 mu mol/l) were significantly lower than those of the control (39.53 +/- 19.43 mu mol/l) and cerebral palsy (77.84 +/- 21.70 mu mol/l) groups. (C) 2000 Elsevier Science B.V. All rights reserved.