We have analyzed the CPK levels in 44 carriers of DMD women, previously diagnosed by using molecular techniques (from a risk population of 133 women), and compare them with the CPK levels of 138 women of a control population. The results obtained show that values higher than the normal level (> 250 mU/ml) are compatible compatible in 99% of the cases with the carrier status (21 women of the carrier population and 1 women of the control population showed values higher than 250 mU/ml). On the other hand, normal values do not distinguish between the healthy and carrier populations (22 women of the carrier population showed normal CPK levels). These results can be very useful in genetic counselling, especially in centers where it is not possible to apply recombinant-DNA techniques.