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Introduction: The recent increase in the number of tuberculosis cases has called the world's attention once again to a perennial health problem, especially prevalent in developing countries. The time elapsed between the diagnosis and the institution of therapy is an obstacle to tuberculosis control and there is an urgent need for the development of techniques for the disease's rapid diagnosis. To achieve this goal, molecular biology techniques have been exhaustively investigated. This work describes the use of a polymerase chain reaction for rapid diagnosis of tuberculosis in a developing country. The sensitivity and specificity of this technique is compared to standard techniques used in the microbiology laboratory., Methods: This study was undertaken in Ribeirão Preto, S. Paulo State, Brazil. Forty-two sputum samples from suspected cases of tuberculosis attending the municipal health care centers were sent to the microbiology laboratory. The samples were processed for the detection of Mycobacterium tuberculosis by acid-fast bacilli determination, culture in Lowenstein-Jensen medium, and by a polymerase chain reaction that amplified a fragment of 123 base pairs of the Mycobacterium tuberculosis genome., Results: Of the forty-two samples studied, one was contaminated and excluded from the study, ten were culture positive, ten were positive for the presence of acid-fast bacilli, and sixteen were polymerase chain reaction positive. The sensitivity and specificity of this technique were 90% and 81%, respectively., Conclusions: The polymerase chain reaction presented a sensitivity comparable to the culture and the whole procedure took only one day to complete. The results presented here make it a strong candidate for rapid diagnosis of tuberculosis in clinical settings making it possible to begin the specific therapy early in the course of the disease. However, standardization of the technique is necessary, and the correlation with clinical findings is of paramount importance due to the high sensitivity of this technique.