We have investigated the effects of GH treatment on bone turnover, bone size, bone mineral density (BMD), and bone mineral content (BMC) in 29 men, 27-62 yr old, with idiopathic osteoporosis. The patients were randomly assigned to treatment with GH, either as continuous treatment with daily injections of 0.4 mg GH/d (group A, n = 14) or as intermittent treatment with 0.8 mg GH/d for 14 d every 3 months (group B, n = 15). All patients were treated with GH for 24 months, with a follow-up period of 12 months, and also received 500 mg calcium and 400 U vitamin D3 daily during all 36 months. Fasting morning urine and serum samples were obtained for assay of IGF-I, bone markers, and routine laboratory tests at baseline, after 1, 12, 24, and 36 months. Body composition, BMD, and BMC were determined by dual-energy x-ray absorptiometry at baseline and every 6 months. After 2 yr, there was an increase in BMD in lumbar spine (by 4.1%) in group A, and in total body (by 2.6%) in group A and (by 2.7%) in group B. BMC of the total body and lean body mass increased, whereas fat mass decreased in both treatment groups. After 36 months, the BMD and BMC in lumbar spine and total body had increased further in both groups. We conclude that 2 yr of intermittent or continuous treatment with GH in men with idiopathic osteoporosis results in an increase in BMD and BMC that is sustained for at least 1 yr post treatment.