The recently introduced automated culture systems MB/BacT (Organon Teknika, Belgium) was compared with radiometric BACTEC 460TB (Becton Dickinson, USA) to test antimicrobial susceptibility of Mycobacterium tuberculosis to first line drugs. On 113 strains 97.5% agreement was obtained, with the difference being not significant. Concordance was practically complete for the most important drugs, isoniazid and rifampin. The two methods however significantly differed for the time needed to complete the test; in fact MB/BacT required on the average five days more than BACTEC 460TB. Despite the delay in the completion of the test, the excellent reliability along with the elimination of radioactivity and full automation make MB/BacT an attractive alternative for susceptibility testing of M. tuberculosis.