In the past eight years, we experienced 94 cases of nontuberculous mycobacteria (NTM) isolation from the specimens of sputum, gastric juice, pleural fluid and fiberoptic bronchoscopic procedure at Chiba Kaihin Municipal Hospital. The species of NTM were M. avium complex (MAC) in 23, M. gordonae in 15, M. kansasii in 12, M. fortuitum in 8, M. chelonae in 7, etc.. The number of isolation of NTM has increased, and it is worthwhile to mention that it had exceeded the number of isolation of M. tuberculosis since 1991. We experienced 28 cases of pulmonary infections caused by NTM during the same period. Thirteen cases were by M. avium complex, 11 cases by M. kansasii, one case by MAC and M. kansasii, one case by M. chelonae and two cases by unidentified NTM. Pulmonary infections by NTM also gradually increased. Thirteen cases (46.4%) had underlying diseases in the respiratory system. Most of them were progressive diseases with cavities and were easily diagnosed by mycobacterial examinations of the specimens such as sputum or gastric juice. We were unable to diagnose 12 cases (42.9%) by mycobacterial examinations. Most of them had no underlying diseases and showed small lesions without cavitation on the chest X-ray. Eight cases were diagnosed by the histopathological examination of TBLB (transbronchial lung biopsy) specimens. In such cases, these procedures were also useful for the early diagnosis. This study indicated the increase of the isolation of NTM and the pulmonary infections by NTM. Once the infections are established, they are progressive, and the early diagnosis of these infections are thought to be important.