There is evidence that the number of non-tuberculous mycobacterium (NTM) cases is increasing at least in some areas of the world and as possible causes of the increase, the followings are pointed out; ageing of the population, improved methods for detecting organisms from clinical specimens, increased physician's awareness on the disease, increased exposure of patients to the source of the organism. In Japan, it has been estimated that the overall incidence of NTM disease is about 3 per 100,000. About 80% of NTM are MAC, and among the remainder, Mycobacterium kansasii is most common in our country. Our hospital located in Fukuoka prefecture in Kyushu, western part of Japan. In this study, clinical data of 24 cases of pulmonary infection caused by Mycobacterium kansasii in our hospital, from 1996 to 2000 were investigated. Primary infection type patients were younger than secondary infection type. Nearly all secondary infection type patients had underlying diseases and complications. Serum total protein and albumin in primary type is lower than that in secondary type. The results of mycobacterial drug sensitivity tests were as follows; for rifampicin, 23 cases were sensitive to 10 micrograms/ml, all cases to 50 micrograms/ml, for ethambutol, 15 cases were sensitive to 2.5 micrograms/ml, 22 cases to 5 micrograms/ml, and for isoniazid, all cases were resistant to 0.1 microgram/ml, 11 cases were sensitive to 1 microgram/ml and 23 cases to 5 micrograms/ml. Sputum cultures of patients treated with drug regimens containing RFP converted to negative within 2 months after starting chemotherapy. Although three patients with serious complications died, other 21 patients improved and showed no relapse at least 6 months after the completion of treatment.