DNA polymorphisms have been widely used as genetic markers for identification of the X chromosome that carries the mutation for Duchenne Muscular Dystrophy (DMD) in affected families, but serious limitations are associated with this approach. The complementary DNA (c-ADN) of the DMD gene has recently been isolated and shown to detect partial gene deletions in a large proportion of patients. We present the study of five DMD families in which we have shown the existence of a partial deletion in the DMD gene in the affected boys. We have evaluated the usefulness of this direct approach to diagnose DMD carriers in these families using the c-DNA derived probes. In all cases we have obtained satisfactory results. The method seems to be more reliable, more rapid and less expensive than linkage studies with DNA polymorphisms.