Plasma and urinary indexes of bone metabolism were studied in 36 children affected by juvenile rheumatoid arthritis (JRA) during 1 year, in order to evaluate the calciotropic hormone levels and bone mass. Children were divided in three groups according to the subtype of JRA: pauciarticular, polyarticular, systemic. Patients of the latter two groups were on corticosteroid treatment. A control group of healthy children (matched for age and sex) was compared. Children affected by pauciarticular disease did not show any difference with respect to controls. In the polyarticular and systemic groups, basal observation revealed decreased levels of 25(OH)D, significantly lower (P less than 0.01) with respect to the control and pauciarticular groups. After one year, 25(OH)D showed a further decrease in the systemic group, while PTH levels were increased. Moreover, bone mineral density values in systemic JRA were significantly lower than values of a matched control group and did not increase as expected during the year. It seems thus possible that severe JRA has an influence on bone mass, perhaps mediated by a decrease in active vitamin D metabolites.