The polyneuropathy, organomegaly, endocrinopathy, M protein, skin changes (POEMS) syndrome is a rare multisystem disorder of obscure pathogenesis associated with osteosclerotic myeloma. Circulating levels of proinflammatory cytokines (tumor necrosis factor-alpha (TNF-alpha) interleukin-1 beta [IL-1 beta], IL-2, IL-6, and interferon-gamma [IFN- gamma]), anti-inflammatory cytokines (transforming growth factor beta 1 [TGF beta 1], IL-4, IL-10, and IL-13), the cytokine carrier protein alpha 2 macroglobulin, IL-1 receptor antagonist (IL-1ra), soluble TNF receptors (sTNFr) p55 and p75, and soluble IL-6 receptor (sIL-6r) were determined in 15 patients with POEMS syndrome and 15 with multiple myeloma. Patients with POEMS syndrome had higher serum levels of IL-1 beta, TNF-alpha, and IL-6 and lower serum levels of TGF beta 1 than did patients with multiple myeloma. Serum levels of IL-2, IL-4, IL-10, IL- 13, IFN-gamma, alpha 2 macroglobulin, and sIL-6r were similar in both groups. IL-1ra and sTNFrs were increased in POEMS syndrome, but out of proportion to the increase of IL-1 beta and TNF-alpha. Serial evaluations in 1 patient showed that proinflammatory cytokine serum levels paralleled disease activity assessed by platelet count and neurologic involvement. Our results suggest that the manifestations of POEMS syndrome might be regarded as the result of a marked activation of the proinflammatory cytokine network (IL-1 beta, IL-6, and TNF- alpha) associated with a weak or even decreased (TGF beta 1) antagonistic reaction insufficient to counteract the noxious effects of cytokines.