In a 2-year study, we examined bone mass and calcium metabolism in 36 elderly women with moderate osteoporosis. The study period comprised 1 year of observation, during which the women received no treatment affecting calcium metabolism, and 1 year of treatment, during which all participants received daily salmon calcitonin (sCT) 100 IU rectally and calcium 500 mg. During the observational period a significant bone loss of 1.5% was seen in the forearm (P less than 0.01), whereas the spinal bone mass was virtually unchanged. After institution of treatment, the bone loss was arrested in the forearm and a significant increase of about 2% was seen in the spine (P less than 0.01). The net effect of treatment revealed a positive outcome in both bone compartments (1.9% and 2.9%, P less than 0.05-0.01). Correspondingly, the parameters of bone turnover (serum alkaline phosphatase, plasma bone Gla protein, and fasting urinary hydroxy-proline/creatinine) did not change during the observational period, but significantly declined, 10-30%, during sCT treatment (P less than 0.01-0.001). Tolerance was generally good, although in one woman, anoscopy revealed irritative changes in the rectal mucosa. We conclude that, given rectally, sCT is well absorbed and well tolerated and that it has a beneficial effect on calcium metabolism in moderately osteoporotic women.