The effects of recombinant human IL-1 beta on the production of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), N-acetyl-beta-D-glucosaminidase (NAG), and superoxide by synovial cells and chondrocytes derived from osteoarthritis patients were determined. IL-1 beta markedly enhanced PGE2 production in chondrocytes and, to the lesser extent, in synovial cells. Synovial cells and chondrocytes spontaneously released LTB4 into culture medium and IL-1 beta significantly inhibited LTB4 production by these cells. IL-1 beta significantly suppressed the release of NAG and superoxide by synovial cells, whereas it significantly enhanced the production of NAG and superoxide by chondrocytes. Production of intracellular superoxide dismutase by synovial cells was significantly enhanced on incubation with IL-1 beta, but that of chondrocytes was not altered. IL-6, unlike IL-1 beta, significantly suppressed the production of NAG and superoxide by synovial cells and chondrocytes. These results suggest that IL-1 has differing effects on the release of mediators by synovial cells and chondrocytes and that these cells also vary in their responses to IL-1 beta and IL-6.