We studied 30 girls (age 6.36 +/- 1.21 years, range 4.6-8.8) affected by idiopathic precocious puberty with significant reduction of height velocity (below the 25th centile) at the end of 1 year of Gn-RHa (triptorelin intramuscular depot) treatment, to evaluate GH-IGF-I axis activity and the effects of combined Gn-RHa plus hGH therapy. After 12 months, 15 patients continued Gn-RHa and started hGH therapy for 12 months, while 15 continued treatment with Gn-RHa alone (control group). We evaluated height velocity, bone age, urinary GH, serum IGF-I and IGFBP-3 levels throughout the study; plasma GHBP levels were determined only in the first 12 months of Gn-RHa treatment. Height velocity decreased significantly during Gn-RHa treatment; it increased significantly and became higher than the control group after 12 months of Gn-RHa plus hGH treatment. During Gn-RHa therapy alone, bone age progressed less than chronological age, while in the 12 months of Gn-RHa plus hGH treatment there was a slight nonsignificant increase in bone age progression in comparison to controls. Serum IGF-I and IGFBP-3 levels decreased significantly at 12 months of Gn-RHa therapy and increased significantly after Gn-RHa plus hGH treatment. Urinary GH levels showed the same behavior. Plasma GH binding to peak II-BP, slightly lower than the prepubertal normal range before treatment, significantly increased after 12 months of Gn-RHa treatment. Therefore, in these girls, during Gn-RHa treatment alone, we have a reduction in GH-IGF-I axis activity. During Gn-RHa plus hGH therapy there was a significant increase in height velocity, in urinary GH levels, in serum IGF-I and IGFBP-3 levels. Bone age did not seem to advance faster than chronological age and this may imply a better prediction in adult height. In our opinion, only in a small percentage of patients affected by precocious puberty (with a very low predicted adult height or an important reduction of growth velocity during Gn-RHa treatment) may an association with hGH therapy be useful.