SYNOPSISAnonymous mycobacteria are now more common than Mycobacterium tuberculosis as causes of both clinical infections and tuberculin sensitization of children in Australia, parts of North America and several European countries. These organisms, although less virulent than M. tuberculosis, are usually resistant to anti-tuberculous drugs. A double Mantoux test, already used extensively in population surveys, has been introduced for routine testing in a Children's Hospital, and has been found helpful in screening for mycobacterial infection and in distinguishing between infections by M. tuberculosis and the anonymous mycobacteria.