The secreted antigens of 24K and 38K and the hsp of 12K and 16K are valuable as reagents in a serodiagnostic assay for tuberculosis. A combination of the TB72 assay with either the 16K or 24K antigen gives the best sensitivity and specificity. Antigens isolated from mycobacterial cultures are valuable in a serological test. Peptides cannot be used as antigens. The value of antigens obtained with recombinant DNA techniques remains to be determined. In HIV-seronegative patients with TB serodiagnosis is a valuable test both in pulmonary and extrapulmonary TB. Unfortunately, the results in HIV-seropositive patients are rather disappointing. The use of likelihood ratios seems to increase the potential of serodiagnostic assays. The value of serodiagnosis should be judged in context with other diagnostic methods such as direct microscopy, bacteriological culture or skin tests. A serological test is especially valuable in cases where direct microscopy, polymerase chain reaction or skin testing is negative and allows antituberculous therapy to be started before results of culture are known.