The administration of androgens to adolescent boys with constitutional delay in growth has been highly controversial because of the possibility of premature epiphyseal closure and reduced final height. We have treated 15 such boys with a mean (+/- SD) age of 14.1 +/- 1.0 years and a mean initial height of 142.2 +/- 8.6 cm (range, 127.1 to 156.2). The boys received monthly intramuscular injections of testosterone enanthate (50 mg) for 1.2 +/- 0.3 years. The mean height velocity rose from the 3rd percentile for mean skeletal age to above the 90th percentile, where it remained throughout treatment. Although skeletal maturation accelerated initially in the seven boys with a skeletal age under the pretreatment group mean of 11.3 years, it advanced normally in the others. The concomitant increase in stature was sufficient to offset the advancement in skeletal age in most boys, so that the mean predicted adult height was essentially unaffected. Sexual maturation also progressed; testicular volume increased from 5.9 +/- 2.7 to 11.3 +/- 2.7 ml. After treatment, the skeletal age advanced normally and sexual development continued. Eight of the boys are now 18.1 +/- 0.5 years of age and have stopped growing; their present mean height (167.6 +/- 4.7 cm) is very close to their pretreatment predicted height of 168.0 +/- 5.6 cm. We conclude that low-dose testosterone treatment is effective in adolescent boys with delayed growth and development and that it does not appear to compromise final adult height.