An investigation (clinical, immunological and epidemiological) of the workers of various fowl-farms was carried out in various regions of Kazakhstan for a number for years; the sera of domestic fowl and birds was studied as well. On the basis of examination of 6264 persons the greatest percentage of ornithosis was revealed among the workers of the slaughter house and the shop for the processing of the fowl. Examination of 4749 sera of bird blood showed that the highest incidence of ornithosis was among doves and ducks (43.2 and 11.6%), and the least--in chickens (5.3%); there proved to be a direct relationship between the infection of man and birds. Thus, it was shown that domestic fowl and also doves served as the source of ornithosis infection; foci of ornithosis were revealed in a number of Kazakhstan regions as a result of these investigations.