Abstract: Objective To investigate the clinical significance of the examination to Mycobacterium tuberculosis L type (MTB L). Methods There were 314 specimens from 314 cases with tuberculos is: 312 portions of sputum, 1 portion of prostatic fluid and 1 portion of semen. The specimens were digested, adjusted PH and then centrifugalized for 30 minutes with 3800 turns per minute. Picked the sediments and inoculated them to 92 TB L and common TB culture bases as the control.The following Results were anal ysised:(1) The positive ratio of MTB L and MTB culture in initial and retreatment cases, extra pulmonary cases and cured cases. (2)The relationship between positive rate of sputum MTB L culture and the duration that patients taking clini cal consultation and the onset of illness of initial pulmonary tuberculosis cases. (3)The relationship between positive rate of sputum MTB L culture and the variety and quantity of the first line TB drugs used before of retreatment pu lmonary tuberculosis cases. Results In 314 cases,the co positive rate of MTB and MTB L culture was 42.4%.The single positive rate of MTB L culture was 28.7%.The case with positive result of MTB L culture in initial cases occupied 64.8% of the total positive cases (59/91) and related with the durati on of clinical consultation. There was significant difference of the positive rates between that of cases who taking clinical consultation exceeding one month and less than one month (P＜0.05). In retreatment cases,the cases with positive result of MTB L culture occupied 72.5% in total retreatment positive cases (29/40) and related to the variety and quantity of the first line TB drugs used before. There was significant difference of positive ratio between 4 drugs and 13 drugs used for more than 3 months (P＜0.01). Conclusions There was great clinical significance of the examin ation to MTB L for diagnosing,judging the activity,assesment the treatment effe ction and guiding the clinical treatment, especially to MTB negative cases.It was important for initial and retreatment patients that they should make clinical consultation timely and be treated regularly to reduce the forming of MTB L.

Key words: Mycobacterium tuberculosis, L type, Examination, Positive ratio