The paper considers the results of histological and bacterioscopic examinations of biopsy specimens from the lung and mediastinal lymph nodes of 120 patients with an unclear diagnosis of tuberculosis and sarcoidosis and with problem of their differential diagnosis. One hundred and five of these patients were microscopically diagnosed as having either tuberculosis or sarcoidosis. Additional examination of differently stained sections and that using immunohistochemical M. tuberculosis detection were conducted in 15 cases, which could diagnose tuberculosis and sarcoidosis in 7 and 8 patients, respectively. Bacterioscopic examination, in terms of extreme variability the phenotypic properties of mycobacteria, is of decisive importance in the differential diagnosis of tuberculosis and sarcoidosis.