Major features of Mycobacterium tuberculosis as the slow metabolism and the large amount of lipid in the outer layer of the cell wall, shown by acid-fast staining, are responsible for its peculiar morphology and pathogenicity. For correct diagnosis of M. tuberculosis infection, direct microscopy of the pathological sample, isolation and identification on suitable culture media of the microorganism and in vitro tests of antituberculous drug sensitivity are required. Alternative time-sparing methods have been proposed: the radiometric system is the most important; other manual or automated systems as indicators of mycobacterial growth have been developed, while the new methods of rapid identification as high-performance liquid chromatography (HPLC) cannot be used as a routine for the high cost of equipment.