Background/Aims. The purpose of this study was to provide information about the in vitro neuritogenesis during cell exposure to extremely low frequency electromagnetic fields (ELF-EMFs) of different intensities and durations using pheochromocytoma-derived cell line (PC12 cells) as neuronal model. Methods. Proliferative rates and neuritogenesis were tested by colorimetric assay and morphological analysis, respectively; reactive oxygen species (ROS) levels and intracellular Ca2+ variations monitored using single cell videomicroscopy. Results. The long-lasting ELF-EMF exposure (0.1-1.0 mT) did not appear to significantly affect the biological response (proliferation and neuritogenesis). However, during the acute ELF-EMF exposure (30 min), in undifferentiated PC12 cells, there were increased ROS levels and decreased catalase activity, that, conversely, resulted increased after chronic exposure (7 days) at 1.0 mT. Acute exposure (0.1-1.0 mT) affected the spontaneous intracellular Ca2+ variations in undifferentiated cells, in which basal intracellular Ca2+ resulted increased after chronic exposure. In addition acute exposure affected cell response to a depolarizing agent, while basal membrane potential was not changed. Conclusion. Even if further studies remain necessary to identify the ROS/intracellular Ca2+cross-talking pathway activated by ELF-EMF exposure, we support the hypothesis that ROS and Ca2+ could be the cellular “primum movens” of the ELF-EMF induced effects on biological systems.