We investigated the relative contribution of lean body mass (LBM) and body fat mass to bone mineral density (BMD) in 93 healthy Japanese male volunteers (mean age, 33.1 +/- 6.9 years; range, 18-54 years). Age, height (Ht), weight (Wt), and body mass index (BMI, Wt/Ht(2)) were recorded. Body fat mass, percentage of body fat, body fat mass/Ht(2), LBM, LBM/Wt, LBM/Ht(2), and lumbar spine (L2-L4) and total body BMD (TBBMD) were measured by dual-energy X-ray absorptiometry. On the Pearson correlation test, LBM was positively correlated with L2-L4 BMD. LBM, LBM/Wt, and LBM/Ht(2) were positively correlated with TBBMD. However, body fat mass and body fat mass/Ht(2) were not correlated with lumbar spine and total body BMD. On the partial correlation test, LBM was still correlated with lumbar spine ( r = 0.307, P < 0.05) and total body BMD ( r = 0.545, P< 0.0001), irrespective of age and height, whereas body fat mass was not correlated with BMD of these sites ( r = -0.069 and -0.169, respectively). We concluded that, in males, LBM is one of the significant determinants of BMD whereas body fat mass is a negligible BMD determinant.