The epidemic of respiratory disease (Legionnaires' disease) occurred after the American Legion convention between 21-24 July 1976 in Philadelphia, USA, similar epidemics occurred previously with unknown etiology in the USA and in England with similar clinical symptoms and pathological findings of the disease, the isolated etiological agent, its morphology culture, pathological findings in laboratory animals, serological and immunofluorescent test, the proposed term for the causative organism (Legionella pneumophila) at the International Symposium on Legionnaires Disease held at the Center for Disease Control in Atlanta, Georgia, USA, on November 13th-15th, 1978 are reviewed.