Exposure to extremely low-frequency (ELF) electromagnetic fields appears to result in a number of important biological changes. In the present study, we evaluated the effects of 60 Hz sinusoidal magnetic fields (MF) at magnetic flux densities of 1.0, 1.5 and 2.0 mT on growth and differentiation of the protozoan Entamoeba invadens. We demonstrated an inhibitory growth effect when trophozoite cultures were exposed to 1.5 and 2.0 mT. Furthermore, we found that there was not a synergistic effect in cultures co-exposed to MF and Metronidazole, a cytotoxic drug against amoebic cells. In addition, MF exposure inhibited the encystation process of E. invadens.