The drug susceptibilities of 105 isolates/strains of Mycobacterium tuberculosis (101 clinical isolates and four control strains from the American Type Culture Collection) were assessed by the MB/BacT system and conventional agar proportion method. The agreement rates between the two methods were 99.0% for streptomycin, 95.2% for isoniazid and 100% for rifampin. The mean times to detection for drug-resistant isolates were 4.7 days (range: 2.5-13.7 days) using the MB/BacT system and 14.8 days (range: 14-21 days) using the agar proportion method. For drug-susceptible isolates, the times to detection were 10.8 days (mean) and 21 days respectively. Thus, these data have demonstrated that the automated, non-radiometric MB/BacT system is an efficient, accurate and reliable method for assessing drug susceptibilities of M. tuberculosis compared with the conventional agar proportion method.