Gonadotropin releasing hormone (GnRH) agonists have shown to be effective in the treatment of several sex-hormone-dependent conditions. However, their use could be limited by the bone loss they induce. To evaluate the use of nasal salmon calcitonin (sCT) in preventing this bone loss, 40 patients with endometriosis were treated for 6 months with triptoreline (3.75 mg monthly) and calcium (1 g daily), and randomized in three groups-placebo, sCT 100 IU daily and sCT 200 IU daily-in a prospective double-masked study. Dual-energy X-ray absorptiometry and biochemical parameters were used to evaluate the benefit of the treatment. At baseline, there were no statistically significant differences between the groups. After 6 months, estradiol and biochemical markers of bone metabolism were at postmenopausal levels, with no difference between the groups. There was no difference in bone loss in the three groups, at all sites. Mean lumbar bone loss was 4.01 +/- 2.59% (mean +/- SD) in this population. In this study dosages of 100 IU and 200 IU daily of nasal sCT were insufficient to prevent bone loss during GnRH agonist treatment.