Although a large number of epidemiological, clinical, and pathological studies on methylmercury intoxication have been published, these investigations have not been able to elucidate the detailed mechanisms by which the metal alkyl causes a wide variety of biological dysfunctions. Thus, the cultured cells which are free from the influence of whole body complexities, such as absorption, distribution, metabolism, etc., which complicate the interpretation of in vivo experimental results, attract the attention of many scientists who are interested in clarifying the mode of toxic action of methylmercury. The aim of this article is to review the recent studies on the toxicity of methylmercury at the cellular level and to outline the mechanisms which have been proposed to be responsible for cell injuries.