Twenty-four women (mean age +/- SD 49 +/- 13 years) with classical or definite rheumatoid arthritis (disease duration 15 +/- 8 years) were treated with synthetic salmon calcitonin (SCT) nasal spray 200 IU three times a week for 3 months. Bone biopsies from the iliac crest were taken before and after SCT treatment. Histomorphometrical quantification of undecalcified bone sections was made using the manual point-counting method. SCT decreased the resorption surface of trabecular bone (ES/BS) significantly (P less than 0.001). There was also a significant increase (P less than 0.05) in trabecular bone volume (BV/TV) after 3 months of treatment, whereas no statistically significant changes were found in osteoid parameters. There were no significant changes in biochemical analyses of bone metabolism. We conclude that SCT might be useful in the prevention of bone loss in RA.