Juvenile rheumatoid arthritis (JRA) is the most frequent pediatric connective tissue disease. It is still unclear if the disease represents a single entity or several diseases with multiple pathogenetic mechanisms. Among the possible causes are infection, trauma, stress, immunogenetic predisposition and autoimmunity. The autoimmune nature of the disease has been supported by: 1) increased frequency of antinuclear antibodies and rheumatoid factor in the sera of these patients, 2) the presence of circulating autoantibodies directed against the T cell subpopulation which induces the generation of suppressor cells, 3) segregation of certain HLA antigens such as HLA-DW5 and HLA-DW-8, and 4) sporadic, not well-documented reports of deficient peripheral immune cell functions. Careful analysis of various cellular immunological functions in vitro using modern more sophisticated immunological techniques is absolutely needed in order to shed light on the immune status of patients with JRA. Major findings to date include: increased numbers of pre-activated B and T lymphocytes in the peripheral blood and altered functions of selected T cell helper and suppressor cell assays. Studies are in progress to identify the pathogenesis of these immunoregulatory disturbances and to identify potential factors which can restore immune function toward normal in JRA patients.