Prolonged elevation of the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) is often attributed to hepatic diseases. However, these enzymes are also present in a variety of extrahepatic tissues, including skeletal muscle. Five children (all boys) were referred to the pediatric department of the National Taiwan University Hospital because of persistent elevation of serum aminotransferase activities. The ages of these children were between 4 months and 5.5 years. The neurological findings were all not remarkable. The initial ALT and AST values were 114-581 U/L and 183-700 U/L, respectively. Serum creatine kinase was checked first after 0 to 30 months follow-up and found to be markedly elevated (range, 10,557 U/L to 62,508 U/L). Muscle biopsies in the five cases all showed degenerating and regenerating myofibers with interstitial fibrosis. In Cases 3, 4 and 5, complete absence of dystrophin immunoreactivity was found. Genetic studies showed deletions in the DMD gene (exons 45-48 in case 2 and 49-50 in case 4). This experience indicates that occult muscle diseases should be taken into account in patients with unexplained long-lasting hypertransaminasemia and therefore measurement of serum creatine kinase activity and muscle biopsy should be done early for the correct diagnosis of muscular dystrophy.