Serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) determinations have been carried out in a sample of 30 obligate carriers for the DMD gene and 50 normal adult control females. In all the subjects under study blood samples have been collected 3 times on 3 independent occasions and the means of these 3 determinations were considered for both CPK and PK activities in the statistical analysis. Discriminant analysis has shown that in the group of 30 obligate carriers the estimated proportions of misclassification using either serum CPK, PK or both enzymes were fourn to be: 10/30 (33.3%) for CPK alone, 6/30 (20%) for PK alone and 5/30 (16.6%) for both enzymes. It is concluded that although a small proportion of carriers still remain undetected the concomitant use of PK and CPK determinations enhances the capability of detecting carriers for the Duchenne gene mainly when compared with CPK alone.