Two hundred and fifty-five postmenopausal women with distal forearm bone mineral density (BMD) 1 SD below the mean value for normal age-matched postmenopausal subjects were randomly allocated to a 2-year treatment with oral ipriflavone (200 mg t.i.d) or a matched placebo, according to a double-masked, parallel group design. All patients also received a 1 g/day calcium supplement. Distal radius BMD and bone metabolism markers were measured at baseline, and every 6 months. Blood haematology and chemistry and physical parameters were monitored at the same time. One hundred and ninety-six patients completed 2 years of treatment. BMD changes from baseline were analysed according to valid completers (VC) and intention to treat (ITT) analyses. In both cases radial BMD was maintained in patients treated with ipriflavone while in decrease in those receiving the placebo, the between-treatment difference being significant at year 1 and year 2. Urinary hydroxyproline/creatinine levels were decreased in the ipriflavone-treated group and increased in the placebo group, with a significant between-treatment difference. Adverse reactions, mainly gastrointestinal, occurred to a similar extent in the two treatment groups.