Abstract: Objective To evaluate the relationship between the sputum collected in different time and the nature on the determination of acid-fast bacillus. Methods The sputum specimens were dyed with Ziehl-Neelsen anti-acid dyeing method,and observed with the microscope. The positive rate and the distribution of acid-fast bacillus at different sputum time and in different nature were studied. Results The positive rate of 7305 sputum specimens varies evidently at different time, such as at once, at night, and in the morning; and the rate also varies for the sputum specimens with different nature, such as caseous, bloody, mucopurulent and saliva. The distribution of 518 smear positive cases at different time and in different nature has great difference. Conclusion The caseous sputum collected in the morning was detected with highest number of bacteria and should be used for diagnosis.

Key words: tuberculosis, pulmonary, sputum, acid-fast bacillus, microscopy