The effect of 50Hz electromagnetic fields on the immune system was assessed by measuring the cytokine production of the peripheral blood mononuclear cells (h-PBMCs) of a healthy individual. The h-PBMCs were exposed in vitro to varying magnetic flux densities of 1, 3, 10, and 30 milliTesla for 3 days. Changes in cytokine production of IL-1β, IL-2, IL-6, IL-10, IFN-γ, and TNF-α were studied using the ELISA method. Significant reduction in TNF-α production by the EMF-exposed h-PBMCs, in comparison with the non-exposed cells, was detected at all exposure levels (p<0.05, p<0.01). Significant increase in IL-1β production and decrease in IFN-γ production were also detected at some exposure strength. No significant differences were detected between the control and the EMF-exposed cells in the production of the other cytokines.