We have recently shown that long-term use of inhaled corticosteroids decreases bone mineral density (BMD) of the lumbar spine in postmenopausal asthmatic women. The present study aimed to evaluate the efficacy of alendronate in comparison with that of alfacalcidol (1-alpha-hydroxyvitamin D(3)) for the treatment of BMD reduction in postmenopausal asthmatic patients who had inhaled corticosteroid therapy without regular use of systemic corticosteroids. Twenty-eight postmenopausal asthmatic patients with BMD T score of -1.0 or less were randomized to receive alendronate (5 mg/d) or alfacalcidol (1 microg/d). Bone mineral density was determined at baseline and 12 months after the treatment, and biochemical markers of bone metabolism were measured at baseline and after 6 and 12 months of treatment. The mean (+/-SD) BMD values at the lumbar spine, the total hip, and the Ward's triangle significantly increased by 4.9 +/- 4.5% (P = .0005), 2.4 +/- 2.2% (P = .0005), and 3.6 +/- 5.2% (P = .02) at 12 months in the alendronate group, whereas the corresponding values did not significantly change in the alfacalcidol group. In the alendronate group, urinary N-telopeptide (NTx), serum osteocalcin, and serum alkaline phosphatase concentrations significantly decreased, and serum intact parathyroid (PTH) level significantly increased, from baseline at both 6 and 12 months. In the alfacalcidol group, urinary NTx showed modest but significant decrease, although the extent of the change was smaller than that in the alendronate group. We concluded that alendronate was effective to improve reduced BMD in postmenopausal asthmatic patients on inhaled corticosteroid therapy through the mechanism of inhibiting bone resorption.