Abstract: Objective To determine the difference on smear negative conversion rates of new smear positive TB patients by 2 smear tests and 3 smear tests.Methods Testswith 2 smear and 3 smear are conducted once a month in the six months of treatment of the new smear positive TB patient 1047.Results During the six months of treatment,the smear negative conversion rates by 2 smear and 3 smear tests at the end of 4th～6th months of treatment are almost the same.The difference was found at the end of 1th and 2nd months.The differences was 4.4% and 3.1% respectively.The relapse rates within two years was 2.4% in cases with negative Results and with intensive treatment for another month,and 9.4% in cases of negative result of 2 smear test at end of the 2nd month but still of positive result of 3 smear test and nit out extended intensive treatment.There was significant difference.Conclusion It is better to conduct follow up sputum tests at the end of month 1 and 2 of tre atment of TB patients by 3 smear tests.

Key words: Sputum smear, Negative result of sputum test, Tuberculosis