In 28 postmenopausal women with rheumatoid arthritis, serum osteocalcin (OC) concentration decreased from 5.2 +/- 1.9 ng/ml to 3.0 +/- 1.6 ng/ml after 6 months therapy with corticosteroids (p less than 0.005). No differences, however, were found in a control group of 13 patients treated for 6 months with nonsteroidal anti-inflammatory drugs. In those patients with serial OC measurements, changes in serum OC were already evident within the first month of therapy. This suggests that a suppressed osteoblast function may be detectable early during corticosteroid therapy in rheumatoid arthritis. Fifteen patients treated with prednisone (5-25 mg once daily, mean 12.33 mg/day) showed a more marked decrease in serum OC than 13 patients treated with equivalent doses of deflazacort (p less than 0.005). Prednisone therapy at doses higher than 10 mg/day resulted in a severe suppression of OC values in most cases. The effect of deflazacort was, however, mild in the majority of patients treated with doses of up to 30 mg/day.