An enzyme-linked immunosorbent assay (ELISA) using Mycobacterium tuberculosis antigen 5 has been evaluated as a serodiagnostic test for active tuberculosis in children. Forty children of either sex, ages 1 to 14 yr, were studied, including 21 bacteriologically confirmed tuberculous patients and 19 control subjects who were evaluated for tuberculosis and found to be free of disease. At a 1:20 dilution, the test showed a sensitivity of 0.857 and a specificity of 1.000, with an accuracy value of 0.925, a positive predictive value of 1.000, and a negative predictive value of 0.864. The prevalence of disease calculated directly from the data of the study was found to be of 0.525. The geometric mean ELISA titer of the tuberculosis group was 1:58, and the difference in antibody titers between patient and control groups was found to be statistically significant (p less than 0.001). From our results, we conclude that ELISA using M. tuberculosis antigen 5 may be useful in those situations of high prevalence of disease when children suspected of tuberculosis are being evaluated.