Minamata is a small industrial town with a total population of about 50,000. It is near the south west coast of Kyushu, the most southerly of the main Japanese islands. There is an old large artificial-fertilizer factory, the effluent from which empties into a small Minamata Bay. In this factory, a small amount of vinyl chloride compounds were experimentally manufactured during 1949-1951, and their production on a large scale has been opened since 1952 to 1953, separately from the fertilizer production. From the end of 1953 a mysterious nervous illness began sporadically to affect the villagers, especially the fishermen, and was called the “Minamata Disease ”. The outbreak was investigated by several departments of our University. The pathologic investigations and experiments were made by us. It was explained that the illness was caused from the eating of a large amount of fish and shellfish contaminated by the effluent of the new industrial department. The toxic agent seems to have some relation to the manufacturing of the vinyl chloride compounds.