Currently, replacement recombinant GH (rGH) therapy in GH-deficient (GHD) adults is performed in daily injections. This modality of treatment is not complied with by the totality of GHD patients, who are supposed to receive life-long replacement. The aim of our study was to compare daily vs. thrice weekly (TIW) rGH injection effects on lipid profile, body composition, bone metabolism, and bone density in 34 GHD patients (13 women and 21 men; median age, 39 yr; range, 30-55 yr) randomly assigned to different therapeutic regimens. Group A included 18 patients receiving daily rGH injections, and group B included 16 patients receiving TIW injections of rGH. The starting dose of rGH was 10 microg/kg x day in both groups. Subsequently, the dose was adjusted to maintain serum insulin-like growth factor I (IGF-I) concentrations in the normal age-adjusted range. IGF-I levels were assessed before and after 1, 3, 6, and 12 months of rGH treatment, and lipid profile, body composition, bone metabolism, and bone density were evaluated before and after 6 and 12 months of treatment. Thirty-four healthy subjects served as controls. In the basal condition, lipid profile, body composition, bone metabolism, and bone density were significantly different in patients compared to controls. Conversely, patients included in groups A and B had similar serum IGF-I levels, lipid profile, body composition, bone metabolism, and bone density. After 3 months of rGH treatment, IGF-I levels were normalized in 15 of 18 patients (83.3%) in group A and in 7 of 16 patients (43.7%) in group B (chi2 = 4.21; P = 0.04). At this time point, serum IGF-I levels in patients in group A (202+/-57.5 microg/L) were significantly higher than those in patients in group B (155+/-45.1 microg/L; P = 0.001). After 6 months of therapy, serum IGF-I levels were normalized in all patients and were similar in both groups (223+/-35.2 vs. 212+/-41.4 microg/L, A vs. B, respectively). IGF-I levels remained normal until the 12-month follow-up. After 6 months of rGH replacement, total cholesterol, low density lipoprotein cholesterol, triglycerides, bioelectrical impedance, and body fat mass were significantly reduced, whereas high density lipoprotein cholesterol levels and lean body mass were significantly increased in both groups of patients, without any difference between them. No further change in lipid profile and body composition was observed after 12 months of treatment. Serum bone GLA protein and procollagen III levels were significantly increased after 6 months, and a downward trend was observed after 12 months of rGH replacement. However, a slight, but significant, increase in bone mineral density was observed in both groups only after 12 months (P = 0.0001). All patients in group B had good compliance to the TIW treatment, whereas 5 patients in group A had poor compliance to the treatment (chi2 = 3.2; P = 0.07). In conclusion, our randomized, prospective, and controlled study confirmed that rGH therapy with TIW injection regimen is effective in normalizing IGF-I levels and improving lipid profile, body composition, bone metabolism, and bone density. It also demonstrated that this efficacy is comparable to that observed in patients treated with daily rhGH therapy, with few side-effects and good compliance.