A child with Wilm's tumor and a child with immune thrombocytopenic purpura (ITP) were each noted to have persistent elevations of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH). Both children underwent thorough evaluation for liver disease and, as a result, experienced delays in treatment of the Wilm's tumor and ITP. Eventually both children were found to have extremely elevated serum creatine kinase (CK). Muscle biopsy confirmed diagnoses of Duchenne's muscular dystrophy in one child, and Becker's muscular dystrophy in the second. Hematologists/oncologists should consider obtaining a serum CK to rule out muscle disease in patients with unexplained elevations of AST, ALT, and LDH. Am. J. Hematol. 66:46–48, 2001. © 2001 Wiley‐Liss, Inc.