Abstract. The potential risks that electromagnetic fields (EMF) pose to human physiology have been debated for several decades, especially considering that EMF is almost omnipresent and some occupations involve regular exposure to particularly strong fields. In the present study, the effects of 60 Hz 0.3 mT EMF on CD4 + T cells were evaluated. Production of T cell related cytokines, IFN-γ and IL-2, was not altered in CD4 + T cells that were exposed to EMF, and cell proliferation was also unaffected. The expression of genes present in a subset of Th17 cells was upregulated following EMF exposure, and the production of effector cytokines of the IL-17A subset also increased. To determine signaling pathways that underlie these effects, phosphorylation of STAT3 and SMAD3, downstream molecules of cytokines critical for Th17 induction, was analyzed. Increased SMAD3 phosphorylation level in cells exposed to EMF, suggesting that SMAD3 may be at least in part causing the increased Th17 cell production. Differentiation of Treg, another CD4 + T cell subset induced by SMAD3 signaling, was also elevated following EMF exposure. These results suggest that 60 Hz 0.3 mT EMF exposure amplifies TGF-β signaling and increases the generation of specific T cell subsets.