The Genentech National Cooperative Study of growth hormone (GH) therapy in Turner's syndrome was initiated in 1983; 70 girls with Turner's syndrome were randomly assigned to observation or to treatment with GH alone, oxandrolone alone, or a combination of GH plus oxandrolone for a period of 12-24 months. After completion of this phase, patients receiving GH alone were continued on GH, while all other patients received the combination of GH plus oxandrolone. Data are currently available on the 62 girls who were treated for a minimum of 3-6 years. When compared with the height velocities anticipated for girls of comparable ages with untreated Turner's syndrome, both GH alone and a combination of GH plus oxandrolone resulted in an increase in height velocity, which was most prominent during the first 2 years of treatment and was sustained for at least 6 years. Although GH therapy is continuing at present in half of the patients, 14 of 17 girls (82%) receiving GH alone and 42 of 45 girls (93%) receiving combination therapy have exceeded their projected adult heights. For the 30 girls who have stopped therapy, the current mean height is 151.9 cm, compared with their original mean projected adult height of 143.8 cm. These results demonstrate that GH therapy can result in short-term (3-6 years) acceleration of growth, as well as in improved adult height.