The effects of 1 year of growth hormone (GH) therapy were studied in 10 subjects with subnormal spontaneous secretion of GH, whose ages ranged from 6.5 to 12.4 years. Height, weight, body fat percentage, total body potassium (TBK), and extracellular water (ECW) were measured prior to initiating the treatment, and thereafter at 6 months (period 1) and 12 months (period 2). Height velocity almost doubled during the year of treatment: 7.8 ± 0.8 and 7.1 ± 0.7 cm/yr (P < .0001) during periods 1 and 2, respectively, as compared with 3.9 ± 0.6 cm/yr pretreatment. Body fat percentage decreased during period 1 to 18.2% ± 4.9%, versus 16.3% ± 4.5% (P < .02), but stabilized thereafter (16.3% ± 4.9%). Mid-arm muscle circumference (MAMC) and TBK increased in accordance with the predicted values for age. Body mineral density (BMD) increased both in absolute and standardized terms. No changes were found in ECW during treatment. We concluded that GH treatment in children with subnormal spontaneous secretion of GH has mainly a lipolytic effect on body composition, and that resistance to the lipolytic effect develops during the course of therapy.