Interleukin 2 (IL-2) production in the CD4/non-T cell autologous mixed lymphocyte reaction (AMLR) was estimated for patients with juvenile rheumatoid arthritis (JRA). A cellular IL-2 assay (CILA) consisting of co-cultures of indicator cells, CTLL-2, added to CD4/non-T cell AMLR cultures was used. As both CD4 and CTLL-2 cell proliferation are IL-2 dependent, results of the CILA assay were taken as a reflection of the total IL-2 in the co-culture. By this assay most patients with JRA had normal IL-2 production. However, five patients with polyarticular disease had both a low AMLR and low levels of IL-2 production. Three of those tested showed little improvement in the AMLR on addition of recombinant IL-2, suggesting decreased responsiveness to IL-2 as well.