Bisphosphonates have been widely used in the treatment of osteoporosis in women, whereas until now there have been few data on their use in men. The aim of this study was to evaluate the effect of a 3-year alendronate treatment on bone mineral density (BMD) and quantitative ultrasound (QUS) in men with primary osteoporosis. We studied 77 osteoporotic men (aged 57.1 +/- 10.8 yrs) who completed a 3-year treatment with alendronate (10 mg/day) plus calcium (1000 mg/day) (n = 39), or calcium alone (n = 38). At baseline and at a 12-month interval, we measured BMD at the lumbar spine and femur (femoral neck and total hip) by DXA (Hologic) and speed of sound (SOS), broadband ultrasound attenuation (BUA) and Stiffness (S) at the os calcis by Achilles plus (Lunar). Alendronate treatment had significantly increased lumbar spine BMD by 4.2% at year 1, by 6.3% at year 2, and 8.8% at year 3. BMD at the femoral neck and total hip had increased by 2.1% and 1.6% at year 1, by 3.2% and 2.9% at year 2, and by 4.2% and 3.9% at year 3, respectively. BUA and Stiffness showed a significant increase in the alendronate-treated group at year 2 (3.2% and 4.9%, respectively) and at year 3 (3.8% and 6%, respectively). BMD at the lumbar spine showed the best longitudinal sensitivity whereas longitudinal sensitivity of both QUS at the heel and femur BMD were similar. In conclusion, this study confirms that alendronate represents an important therapeutic advance in the management of male osteoporosis. BMD at the lumbar spine appears to be the best method for monitoring the effect of alendronate on bone mass in osteoporotic men.