DNA studies (restriction fragment length polymorphism linkage analysis and deletion analysis with pERT87) and serum creatine kinase/pyruvate kinase (CK/PK) measurements were done to determine the carrier status of 59 mothers and sisters of isolated Duchenne dystrophy (DD) cases. The results of DNA studies modified the carrier risks for 34 of the 59 (58%), but the derived risks often did not differ importantly from risks calculated by conventional methods. Elevated CK/PK provided strong evidence of the carrier state for 24 of the 59 (41%), and CK/PK frequently provided data unavailable through DNA studies. Serum enzyme determinations remain an important means of evaluating DD carrier suspects and are especially valuable in isolated-case families. Enzyme testing should be combined with DNA studies to achieve the best estimate of carrier risk.