The purpose of the present study was to investigate the relationships among physical activity, metacarpal bone mineral density (BMD), and bone resorption marker in healthy active adult men. Seventy healthy men (mean age, 68.4 years, range, 48-85 years) were recruited. The metacarpal BMD of the nondominant hand was measured by computed X-ray densitometry, and the levels of urinary cross-linked N-telopeptides of type I collagen (NTx), as a marker of bone resorption, were measured with an enzyme-linked immunosorbent assay. The relationships among BMD, urinary NTx levels, and activities in leisure time and at work were examined. BMD was 2.77 +/-0.48 (mean+/- SD; range, 1.54-3.60) mmAl, and NTx levels were 44.9 +/-21.0 (range, 11.7 - 91.0) nmol BCE/mmol creatinine. Single regression analysis showed that BMD was significantly correlated with NTx levels and activity at work (r = - 0.331 and P < 0.01; r = 0.468 and P < 0.05, respectively), while NTx levels were significantly correlated with activities in leisure time and at work (r = -0.250 and P < 0.01; r = -0.325 and P < 0.01, respectively). NTx levels were decreased and BMD were increased with higher activity at work. The present study shows that increased physical activity as a result of hard work may have the potential to decrease bone resorption and increase BMD in healthy adult men.