We investigated the levels of circulating CD5+ B cells in 43 patients with seronegative, HLA-B27 negative juvenile arthritis, 7 patients with juvenile dermatomyositis (DM) and 16 children with systemic lupus erythematosus (SLE). We found that CD5+ B cell levels were high in juvenile arthritis (p less than 0.01), normal in juvenile DM and decreased in SLE (p less than 0.01) compared to 33 age matched controls. In juvenile arthritis, the increase of CD5+ B cells appeared to be independent of discuss activity and was present in all the onset types except in a subset of patient with late onset pauciarthritis.