We have evaluated the serodiagnosis of tuberculosis in children using mycobacterial sonicates in an enzyme-linked immunosorbent assay (TB ELISA), a method reported to have been used with success in adults. Attempts were also made to ascertain if prior BCG immunisation would influence the outcome of the test. Using clinically diagnosed and notified cases of tuberculosis as well as subjects in whom the condition had been excluded as controls, it was found that the TB ELISA showed very low degrees of specificity and sensitivity and consequently was not suitable as a diagnostic tool in identifying children aged 5 years or less with tuberculosis. In groups of older children the TB ELISA appeared to be much more promising and gave results more in keeping with those found in adults. In very young infants who were free from tuberculosis we showed that there was a cross reactivity with BCG. Thus it appears that, at present, serodiagnosis of tuberculosis in children is not practical.