Epidemiology of nonspecific pulmonary diseases in the Transbaikal region was studied with regard to the extremal climatic conditions, industrial specificity, and mass migration of the population to the construction sites of the Baikal-Amur railway (BAR). A total of 7.495 persons were examined. Of these, the population of the northern regions accounted for 39 percent, the workers of the mining integrated works for 9.1 percent, and builders of the BAR for 51.9 percent. The persons examined were divided into 3 groups. Group I was constituted by normal persons, group II by subjects with a disease risk (a premorbid group), and group III included patients suffering from chronic nonspecific pulmonary diseases (CNPD). It has been shown that in the region under study, the disease was encountered in 20.2 percent of the local population, in 30.6 percent of the natives (Evenks), in 35.5 percent of the workers of the mining industry. and in 6 percent of the builders of the BAR. In the newcomers, acute pneumonia ran a graver course and was encountered 1.5 times more frequently than in the natives, that was connected with alterations in the people's immune status during adaptation. The risk factors of CNPD development in the region were as follows: industrial occupational hazards, tobacco-smoking, age and length of service, extremal climato-meteorological conditions, chronic diseases of the ENT organs, respiratory diseases experienced in childhood, migration of the population from other climatic areas, and alcohol abuse. The risk factors were enumerated in accordance with their significance.