The main objective of this study was to determine the effect of daily oral alendronate treatment on bone mass in postmenopausal women affected by osteoporosis. The efficacy of intranasal salmon calcitonin was also examined. Nine centers in Italy enrolled 286 postmenopausal women between the ages of 48 and 76 with spinal bone mineral density > or = 2 SD below adult mean peak in the two-year, double-blind, randomized, placebo-controlled trial. Patients were randomized to one of four treatment arms: double-blind placebo, alendronate 10 mg/day, alendronate 20 mg/day, or open-label intranasal salmon calcitonin 100 IU/day; all patients received 500 mg Ca++ supplements. Bone mass was measured by dual-energy x-ray absorptiometry every six months for two years. Patients who received alendronate 10 or 20 mg experienced significant increases in bone mass at all sites measured. At the end of the second year, the mean percent changes, for alendronate 10 and 20 mg relative to placebo, were 5.2% and 7.3% at the lumbar spine, 3.8% and 4.6% at the femoral neck, and 7.1% and 7.5% at the trochanter, respectively. In contrast, intranasal salmon calcitonin failed to increase bone mineral mass significantly at any site. Both alendronate doses significantly decreased serum alkaline phosphatase, serum osteocalcin, and urinary pyridinolines, markers of bone turnover, whereas placebo and intranasal calcitonin did not. Alendronate was generally well tolerated and no serious adverse events were attributed to its use.(ABSTRACT TRUNCATED AT 250 WORDS)