OBJECTIVE:To analyse the distribution of polymorphism of the collagen type Ialpha1 gene (COL1A1) and its relationship with bone metabolism and bone turnover in men with idiopathic osteoporosis. METHODS:A total of 35 male patients with idiopathic osteoporosis, aged 50.4 +/- 10.3 yr, and 60 healthy males (controls), aged 47 +/- 17 yr, were included in the study. Serum osteocalcin, 25-hydroxyvitamin D and parathyroid hormone were determined in all patients. The COL1A1 Sp1 genotypes (SS, SS:, ss) were assessed by restriction enzyme digestion (BAL:1) of DNA amplified by the polymerase chain reaction. RESULTS:Patients with idiopathic osteoporosis had a higher frequency of the s allele than men in the control group (29 vs 11%, P: = 0.003) and a higher frequency of the SS: genotype (patients, 48% SS, 46% SS:, 6% ss; controls, 80% SS, 18% SS:, 2% ss; P: = 0.003). No significant differences between genotypes were observed in serum concentrations of osteocalcin, vitamin D or parathyroid hormone among either the patients or the controls. CONCLUSION:This study suggests that, in men with idiopathic osteoporosis, there is a high prevalence of the s allele and the SS: genotype that is unrelated to other parameters of bone metabolism.