 The prevalence of allergic and autoimmune diseases is increasing in developed countries, possibly due to reduced exposure to microorganisms in childhood, hygiene hypothesis. Epidemiological and experimental evidence in support of this hypothesis is accumulating. In this context, parasitic helminths are now important candidates for anti-allergic, anti-inflammatory agents. Here we summarize anti-allergic anti-inflammatory effects of helminths together along with our own study of the effects of schistosomomansoni on Th17, dependent experimental arthritis. We also discuss possible mechanisms of helminth-induced suppression according to the recent advances of immunology. This article was authored by Yeshio Osada and Tomatsu Konozawa.