Prostaglandin E levels have previously been demonstrated to be elevated in multiple sclerosis (MS). We have further investigated other products of activated macrophages related to inflammation. We report here on prostaglandin E and its relationship to interleukin 1, tumor necrosis factor, and leukotriene B₄ produced by macrophages from blood and cerebrospinal fluid of MS patients and controlsin vitro. Interleukin and tumor necrosis factor are elevated significantly after stimulation in MS, while leukotriene B4 production by blood macrophages is depressed compared to other neurological disease and normal healthy controls. In 40% of MS patients tested, peripheral blood macrophages spontaneously produced elevated levels of interleukin 1. All mediators of inflammation are produced in increased amounts by MS cerebrospinal fluid leukocytes after stimulation. Macrophages from MS blood are not as sensitive as controls to nonsteroidal inhibitors specific for lipoxygenase or cyclo-oxygenase pathways. Positive correlations of elevations in production of such mediators of inflammation as prostaglandin E, interleukin 1, and tumor necrosis factor in MS were significant. Elevated production of these mediators in combination with insensitivity to inhibitors of inflammation suggests a role for activated macrophages in the demyelination process.