Five hundreds and five cases of Mycobacterium tuberculosis infection admitted to our hospital during 7 years from 1993 to 1999. Numbers of newly diagnosed cases were 390, of which 329 (84.4 %) were bacilli positive with sputum examination on admission. The recurrent cases were 115, of which 55 (47.8 %) were bacilli positive cases. During the same period, mycobacteria other than tuberculosis (atypical mycobacteria) were detected in the sputum of other 121 cases. The 63 (52.1 %) out of these 121 cases were diagnosed as atypical mycobacteriosis (AM) due to repetitive detection of bacilli with fulfilled the criteria according to the Japanese Mycobacteriosis Research Group of the National Chest Hospitals. The ratio of63 AM cases to 329 bacilli positive TB cases was 19.1 %, but it range from 8.2 %to 31.3 % year by year.
In these 63 AM cases, 9 (14.3 %) cases excreted AM bacilli simultaneously or alternately with TB bacilli. The other 15 (23.8 %) cases excreted different AM bacilli simulta neously or alternately. The changes or combinations with M. avium and M. intracellulare were most frequently observed (in 12 cases). The manners of changes and combinations with different species weredescribed in detail.
