Peripheral blood lymphocyte subset levels were analyzed in 28 patients with active, polyarticular, juvenile chronic arthritis and in 12 healthy control children. The patients with a similar treatment were divided into two groups, at the beginning of disease and after five years' course. Ten children with juvenile chronic arthritis were treated by glucocorticosteroid. After five years the percentage of active T cells, T suppressor cells and active/total T cells ratio were significantly elevated and there was a decrease in the T4/T8 ratio. Glucocorticosteroids increased the proportion of active T cells but did not change the percentage of other lymphocyte subsets. It is concluded that during the course of disease a drug-induced or spontaneous process appears which corrects the initial immunological disturbance.