The polymerase chain reaction (PCR) using oligonucleotides based on the repetitive sequence (IS6110) of Mycobacterium tuberculosis as a primer was evaluated for detection of M.tuberculosis in clinical samples. We tested 55 clinical specimens from patients suspected of having tuberculosis and 71 specimens from control subjects. PCR was more sensitive than culture (positivity rate was 14.5% and 36.3%, respectively, in suspected patients). This approach to the diagnosis of tuberculosis is a valid diagnostic alternative to classical procedures.