The effects of oral alendronate treatment on spinal bone mineral density and biochemical markers of bone turnover were assessed in women in the early postmenopausal period. Sixty-five women were treated with placebo or 5, 20, or 40 mg alendronate daily for 6 weeks in a double blind study. Treatment with alendronate decreased both urinary markers of bone resorption (pyridinolines, hydroxyproline, and calcium) and serum markers of bone formation (osteocalcin and alkaline phosphatase) in a dose-dependent fashion. This short term treatment with alendronate also produced a dose-dependent increase in lumbar bone mineral density measured 7.5 months after the completion of therapy. Median percent changes in integral spinal bone mineral density, as assessed by dual x-ray absorptiometry, were -2.3, -1.2, +0.7, and +1.2 after treatment with placebo and 5, 20, and 40 mg alendronate, respectively. Treatment with alendronate was well tolerated and produced no fever; gastrointestinal intolerance was no more common than with placebo treatment. Short term alendronate treatment in early postmenopausal women decreased bone turnover and increased vertebral density.