The protective effect of vitamin E on the neurotoxicity of methylmercury was investigated by means of light and electron microscopy. Young male golden hamsters were exposed to 2.0 ppm methylmercury chloride with or without concurrent administration of vitamin E (2.0 ppm). No toxic symptoms were observed in the vitamin E-protected animals while all the animals given methylmercury alone developed severe symptoms of methylmercury poisoning. Light microscopy revealed no significant neural damage by mercury in those animals exposed to methylmercury/vitamin E while significant neuronal necrosis could be demonstrated in both the cerebellum and calcarine cortex of the methylmercury-treated animals. Besides some accumulation of lysosomes, electron microscopy also demonstrated remarkable intactness of the cellular organelles in the nerve cells without neuronal necrosis. It appears that vitamin E has a strong protective potential against the toxicity of methylmercury.