Eighty-four out of 100 enrolled female patients affected by osteoporosis completed a double-blind, randomized trial, using ipriflavone (IP) in a dose of 3 x 200 mg/day (41 patients) or placebo (P)(43 patients). All patients received 1 g/day oral calcium supplementation. Inclusion criteria were: age over 65 years; at least one vertebral fracture in the past; bone mineral density measured at the distal tenth of the radius lower than the normal average -2 x S.D. The trial period was between June 1990 and November 1993. Patients of the IP group showed a significant increase in bone mineral density (P < 0.05) compared with the starting values during the whole study period. Pain decreased rapidly, intake of analgesics dropped, and often significant decreases in calciuria, hydroxyprolinuria, alkaline phospatase, osteocalcin and parathormone values were observed. Only two new fractures occurred during the trial in the IP group. Patients of the P group at the end of the study displayed decreased bone mineral densities (P < 0.05), increased pain, greater consumption of analgesics, and often significant increases in the bone metabolism parameters listed for the IP group. In the