Background: Environmental insults may be factors predisposing to or triggering amyotrophic lateral sclerosis. But, to date, none has been identified. Some epidemiological studies have suggested that occupational exposure to electromagnetic field (EMF) is associated with ALS (1–5). Objectives: To evaluate for the first time, whether exposure of SOD-1 mice to 50 Hz magnetic fields (MF) could activate ALS processes. Methods: SOD-1 mice were purchased from Jackson Laboratories (USA). Eight mice per group were exposed to 50 Hz MF at two levels (100 and 1000 mT). Exposures began before the onset of ALS clinical signs at 10 weeks. Exposure lasted 2 hours/day, 5 days/week for 7 weeks. Sham-exposed mice (placed in inactive coils) were included in this protocol. Body weight, survival, and motor impairment using the Rotarod test (15 rpm, 180 s) were monitored. Mice were sacrificed when they were unable to roll over within 30 sec after being pushed to their side, and this time point was recorded as the time of death. Mice were perfused transcardially with PBS-heparin, followed by 4% paraformal-dehyde in PBS. The brain and the spinal cord were dissected, cryoprotected in 20% sucrose and kept at 280°C until immunolabelling. Immunohistochemistry analyses of brain and spinal cord sections are being conducted to detect radical stress markers. Results: In the exposed groups, no significant differences were measured, as compared to the sham-exposed animals, on the following parameters: weight, Rotarod test and survival. Discussion and conclusions: 50Hz magnetic fields at two exposure levels do not seem to modify ALS progression. Available experimental data do thus not provide evidence for any link between occupational exposure to EMF and ALS. Our data complement those from epidemiological studies related to risk assessment of neurodegenerative diseases in populations occupationally exposed to MF