Serum creatine kinase levels were determined in 75 girls (age range, one month to 15 years) and 200 normal adult women (age range, 18 to 50 years). The values ranged from 12.5 to 80 IU/1 in girls and 19 to 155 IU/1 in adult females. The SCK level appeared to increase with age from 1 to 15 years, after which the level remained fairly constant. These data should be helpful in the detection of carriers of X-linked forms of muscular dystrophy.
