One hundred women on inhaled steroid therapy (dose range from 800 to <1600 microg per day) were randomized to receive 10 mg of oral alendronate or placebo (with 500 mg of calcium in the form of daily calcium carbonate). Bone mineral density (BMD) was measured at baseline, 6 months, and 12 months. The percentage changes in BMD were -0.80% in the placebo group and 2.99% in the alendronate group at the spine (p < 0.001 by analysis of covariance [ANCOVA]), and were -0.51% in the placebo group and 0.97% in the alendronate group at the femoral neck (p < 0.05 by ANCOVA). Five patients in the alendronate-treated group, and a similar number of patients in the placebo group, complained of mild gastric discomfort. We conclude that women on inhaled steroid therapy were at risk of accelerated bone loss, which could be prevented by a daily dose of 10 mg of alendronate.