In order to study the benefit of adding recombinant human growth hormone (rhGH) to antiresorptive therapy, six patients with idiopathic osteoporosis (IO) receiving alendronate plus calcium and vitamin D were started on daily subcutaneous injections of rhGH 2.0 IU for one year. Fasting morning urine and serum samples were collected for N telopeptide of type-1 collagen (NTX), serum bone-specific alkaline phosphatase (BSAP) and insulin-like growth factor 1 (IGF-1) during the study. Bone mineral density (BMD) was determined by dual-energy x-ray absorptiometry at baseline and 01 year. The effect of rhGH was evaluated comparing the percentage changes in BMD during the last year on ALN with the results obtained with the combined therapy. Serum IGF-1 increased in all patients but variations were not significant (p=0.266). Serum BSAP did not significantly change (p=0.078) but median NTX increased at 45 days from 12.3 to 19.8 nMBCE/mMCr (p=0.012) and tended to return to baseline values at 12 months (15.2 nMBCE/mMCr). Comparing with isolated ALN therapy, a beneficial effect on bone density was observed in 2/3 of the patients at lumbar spine, and percentage change (median and quartiles) varied from -0.65% (-2.33 and 2.23) on ALN to 0.70% (-0.35 and 3.03) on ALN+GH. Although no bone gain occurred at the femoral neck, our data point to a positive effect of rhGH in patients with idiopathic osteoporosis.