The effect of 50 Hz 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 milli Tesla for 3 days. Changes in cytokine production of IL-1 beta, IL-2, IL-6, IL-10, IFN-gamma, and TNF-alpha were studied using the ELISA method. Significant reduction in TNF-alpha 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-1 beta production and decrease in IFN-gamma 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.