Bone mineral density of the non-dominant forearm was measured by single-photon absorptiometry at a proximal site (PBMD) and at a more distal site (DBMC) in 9 competitive male swimmers, aged 18 to 23 years, who had been training for 12 +/- 2 years, 10.3 +/- 5.6 hours a week. The results were compared with 25 age-matched controls. PBMD was m +/- SD 0.57 +/- 0.02 g/cm2 in the swimmers and 0.57 +/- 0.05 g/cm2 in the controls. DBMD was 0.45 +/- 0.02 g/cm2 in the swimmers and 0.45 +/- 0.03 g/cm2 in the controls. No difference was found between the two groups. We can therefore conclude that swimming, in absence of gravity, didn't provide our athletes with an effective mechanical load capable to increase bone density of the forearm.