Tuberculosis represents a great world public health problem due to its increased incidence and the advent of multidrug-resistant strains. Recent developments in molecular microbiology have raised hopes about the possibilities of new strategies for tuberculosis diagnosis. Nucleic acid amplification of target molecules to a detectable level is the best developed and the best analyzed system for detecting mycobacteria. A variety of different amplification techniques has been described recently. Although these techniques promise to reduce the time for diagnosis from weeks to hours, their main drawback is lower sensitivity in comparison to the culture. Besides their potential value in diagnosis, amplification techniques offer the possibility of a rapid identification and drug susceptibility determination. Their application in other fields such as epidemiology, could benefit the control of tuberculosis indirectly. This article presents a brief overview of the principles of molecular diagnosis of tuberculosis, summarizes some of the application problems, and describes three recently developed commercial amplification tests based on polymerase chain reaction or transcription-mediated RNA amplification.