OBJECTIVE To explore useful methods for detecting M. tuberculosis in the air of inpatient's wards of tuberculosis. METHODS Thirty samples were collected by using LWC-I air sampler from the air of wards housing sputum positive patients. The samples were washed with 0.85% sodium chloride solution, then centrifuged, and finally detected M. tuberculosis by L-J medium culture, BACTEC method, guinea pig experiment, PCR and Southern blotting. RESULTS The positive rates by PCR and Southern blotting were 47% (14/30) and 60% (18/30) respectively. In the experimental group containing 30 guinea pigs, two were positive by culture from the animal tissues (spleens or lungs), and another one was pathologically positive. Ten guinea pigs in control group were negative. Thirty samples were all negative by L-J and BACTEC. CONCLUSIONS It is indicated that using air sampling to detect M. tuberculosis in the air is practicable. PCR and Southern blotting are very helpful in detecting M. tuberculosis in the air because they have the advantages of high sensibility and specificity, and they remarkably shorten the time of detection. Animal experiment can provide compensation to PCR and Southern blotting.