blood mononuclear cells of a large number of patients with FMS to those of healthy matched individuals. Plasma and peripheral blood mononuclear cells (PBMC) were collected from 110 patients with the clinical diagnosis of FMS and 91 healthy donors. Parallel samples of PBMC were cultured overnight in medium alone or in the presence of mitogenic activators; PHA or PMA in combination with ionomycin. The cytokine concentrations of IFN-gamma, IL5, IL-6, IL-8, IL-10, MIP-1beta, MCP-1, and MIP1alpha in plasma as well as in cultured supernatants were determined using a multiplex immunoassay using bead array technology. As a result, cytokine levels of stimulated PBMC cultures of healthy control subjects were significantly increased as compared to matched non-stimulated PBMC cultures. In contrast, the concentrations of most cytokines were lower in stimulated samples from patients with FMS compared to controls. The decreases of cytokine concentrations in patients samples ranged from 1.5-fold for MIP-1beta to 10.2-fold for IL-6 in PHA challenges. In PMA challenges, we observed 1.8 to 4-fold decreases in the concentrations of cytokines in patient samples. in summary, the cytokine responses to mitogenic activators of PBMC isolated from patients with FMS were significantly lower than those of healthy individuals, implying that cellmediated immunity could be impaired in FMS patients. The authors conclude, that his novel cytokine assay reveals unique and valuable immunologic traits, which, when combined with clinical patterns, could offer a diagnostic methodology in FMS.