Background : PCR technique is useful in diagnosis of pulmonary tuberculosis. But, its sensitivity and specificity is some different among several studies. Our aim is compare our PCR results with other's previous PCR results in AFB smear negative patients. Methods : PCR were performed in patients that their disease were suspected as active pulmonary tuberculosis and that their initial serial sputum AFB smear results were negative. Total number of patients studied by PCR technique was 177. Also, we analyzed the data only in patients whose bronchial washing fluid AFB smear was negative. And the primer had been used was IS 6110. RESULTS: In our retrograde study, the number of patients who are diagnosed as having active pulmonary tuberculosis, inactive pulmonary tuberculosis and nontuberculous pulmonary disease was 99, 28, 50, respectively. In the sputum study, the sensitivity of PCR is 41.5% (27 PCR positive cases/65 active TBc cases). And the sensitivity of TB culture is 53.8% (35 TB culture positive cases/65 active TBc cases). In the bronchial washing specimen study, the sensitivity of PCR is 53.8% (21 PCR positive cases/39 active TBc cases). And the sensitivity of TB culture is 43.6% (17 TB culture positive cases/39 active TBc cases). The specificity of PCR in our study is 94.9%. (74 PCR negative cases/78 inactive TBc or nontuberculous cases) In the cases of patients who were never takened anti-TBc medication, the sensitivity of PCR (45.6% --25 positive cases/55 cases) is some lower than culture (58.2% --32 positive cases/55 cases). In the cases of patients who had been takened anti-TBC medication, the sensitivity of PCR (60% --18 positive cases/30 cases) is some superior than culture (50% --15 positive cases/30 cases). CONCLUSION: We think that PCR results in cases of sputum AFB smear negative patients is nearly same as culture. And PCR is especially useful in patients who had been takened anti-The medication on admission.