To assess whether exposure to excessive adrenal androgens increases muscle strength in girls with congenital adrenal hyperplasia, eighteen girls with 21 hydroxylase type congenital adrenal hyperplasia (CAH), aged 4.3-12.1 years were studied and compared with 78 healthy control girls aged 4-16 years. Maximum voluntary isometric strength was measured using a muscle testing chair, and the highest value from at least three attempts with each leg was recorded. Height and weight were also measured in the patients and controls. When compared with normal girls of similar age, some of the girls with CAH seemed unusually strong, but this difference was less marked when the CAH girls were compared with controls of similar weights. However, our data suggest that girls diagnosed later in childhood may have unusual muscle strength.