In this report we describe the use of dystrophin analysis both in the diagnosis of Duchenne muscular dystrophy (DMD) in an aborted fetus and in genetic counseling. Our consultand's initial carrier risk, as based on family history and creatine kinase determinations, was calculated as 0.6%. DNA analysis of her family (and fetus) modified this risk to 8.5%. Skeletal muscle of the 23-wk male abortus was found to be histologically indistinguishable from that of age-matched controls. However, immunoblot testing for dystrophin indicated that the fetus had indeed inherited dystrophin deficiency. The carrier risk of the consultand was thus elevated to 100%. Dystrophin assays should be employed whenever the diagnosis of fetal DMD is equivocal (e.g., cases in which a gene deletion cannot be identified). Assay results are crucial for genetic counseling for subsequent pregnancies and for studies of the early pathogenesis of muscular dystrophy.