The disruption of melatonin secretion has been largely studied since it could provide the missing link between the exposure to 50/60-Hz electric and magnetic fields (EMF) and the occurrence of possible health effects as the "melatonin hypothesis". We analysed the current experimental data from animal (rodents) where contradictory results have been observed, and from human studies conducted with volunteers or with workers in various conditions of exposure, biological endpoints and metrics. In humans, even in long lasting exposures, the overall results of these studies do not support the "melatonin hypothesis". It is unlikely that malignancies or mood disorders reported by people exposed to 50/60-Hz EMF could be related to the disruption of the melatonin levels.