278 BACTEC MYCO/F lytic system blood cultures for mycobacteria were evaluated between 1997 and 1999. Sixty of them were read as positive by the system, being considered 15 of them as false positives. Twenty-seven yielded mycobacterial growth (13 Mycobacterium avium from 3 patients and 14 Mycobacterium tuberculosis from 8 patients). Other bacteria isolated were coagulase-negative Staphylococcus (13 samples), Corynebacterium sp. (5 samples), Salmonella enteritidis (2 samples) and Klebsiella pneumoniae (1 sample). Five of these isolates were considered as true episodes of bacteremia. The average time for detection of mycobacteria was 12.6 days for M. avium and 26.4 days for M. tuberculosis. BACTEC MYCO/F lytic system is useful for detection of mycobacteremia in clinical microbiology laboratories.