Tuberculin testing is the major method of diagnosing tuberculous infection. Although a significant degree of variability exists in reading reactions (1), the test continues to be the most reliable and available in diagnosis. It is used to diagnose tuberculous infection in contrast to tuberculous disease. Its reactivity separates the infected individual (class 2 — significant skin test with negative bacteriologic and roent-genographic studies) from the exposed individual without infection (class 1 — tuberculosis-exposed history with nonsignificant tuberculin skin test). The implication of a significant tuberculin test is infection with tubercle bacilli.