• Testosterone treatment is known to improve growth hormone (GH) secretion in boys with constitutional delay (CD). To determine whether spontaneous GH secretion is normal after treatment, we assessed GH secretion before and after a four- to five-month course of testosterone enanthate in eight adolescents with CD. Before testosterone therapy, the mean (±1 SD) 24-hour integrated concentration of GH (IC-GH) by constant blood withdrawal technique was 1.7±1.0 μg/L (normal range for age, 3.2 to 11.5 μg/L), and the IC-testosterone was 1.8±2.7 nmol/L. Two patients restudied during treatment had normal IC-GH values. After testosterone treatment, the mean IC-GH of the entire group was 3.3±2.6 μg/L, and the IC-testosterone was 6.5±5.3 nmol/L. Five of eight patients had IC-GH values that were again subnormal. A subnormal IC-GH associated with CD may persist after testosterone therapy is discontinued. Deficiency of spontaneous GH secretion may contribute to short stature and slower growth rates in this patient group. Whether GH therapy in these patients would have a beneficial effect on final height is unknown.