New technologies for the rapid diagnosis of tuberculosis that can be applied in developing countries where the prevalence of tuberculosis is high are based on methods that permit recognition of either mycobacterial products in clinical specimens or specific host responses to mycobacteria. Mycobacterial antigens can be identified by immunoassays based on the enzyme-linked immunosorbent assay (ELISA). Mycobacterial DNA or rRNA can be identified with the use of single-stranded DNA probes. Both techniques are potentially suitable for use in developing countries, although there remain technical problems associated with the use of sputum samples. Serodiagnosis by ELISA is a promising technique based on recognition of the IgG antibody response of the host. The technique is ready for early application and can be used in developing countries. However, high specificity depends on the use of antigens that are not now generally available. The predictive accuracy of any newly proposed diagnostic technique must be compared with that of direct microscopic examination of sputum.