Juxtaarticular osteoporosis is a recognized clinical feature in both rheumatoid arthritis (RA) and psoriatic arthritis (PA), while generalised osteopenia seems to be characteristic of RA only. To assess differences in bone turnover in the two forms of disease, we measured serum osteocalcin levels and other parameters of bone metabolism in two groups of female, ambulant, age-matched patients suffering from active RA or active PA and never treated with steroid therapy. Serum osteocalcin levels were significantly higher in RA patients than in PA patients (13.05 +/- 1.27 ng/ml vs 4.83 +/- 0.88 ng/ml; p less than 0.001), with a significant positive correlation between osteocalcin and serum alkaline phosphatase in both groups. These data suggest that bone turnover is higher in active RA than in active PA. Juxtaarticular osteoporosis could be mediated by local disease mechanisms both in RA and in PA, while factors specifically related to active RA seem to determine a more generalized impairment of bone turnover.