Early detection of active cases of tuberculosis and leprosy remains an important objective for improved implementation of chemotherapy and for reduction in the spread of infection. Progress, in terms of specificity and sensitivity, in immunological methods for the detection of antibodies and antigen has been achieved mainly with the aid of monoclonal antibodies directed against immunodominant species-specific antigen determinants. Competition immunoassays have the advantage of epitope-specificity without the purification of the corresponding determinant structure and have been standardised through careful definition of cut-off points. Whilst a high diagnostic score (about 90%) could be achieved in smear-positive tuberculosis and lepromatous leprosy, antibody levels in paucibacillary disease have so far been of low predictive value