The MB/BacT is a fully automated, rapid, non-radiometric system, for the culture of Mycobacteria for clinical samples other than blood. CO2 production is measured and reported as reflective units from the MB/BacT Process Bottle colorimetric sensor. We are evaluating the MB/BacT system in comparison to our routine culture method--culture on egg media (glycerol and puruvate), in the Bactec 460-Tb radiometric machine and in MB Redox. A total of 286 clinical samples from respiratory tract were inoculated into three or four culture systems and incubated at 37 degrees C. There was only little difference in mean time to detection between the MB/BacT and Bactec system (for M.tuberculosis 11 days versus 9 days), but both systems were faster than egg media (16 days). Contamination rates for MB/BacT system was 8.4%, and for Bactec 6.9%. The colorimetric technology used in the MB/BacT is a rapid and sensitive for the measurement of mycobacterial growth.