Tuberculosis is responsible for more then 2 million deaths worldwide each year 
and vies with HIV as the world's most fatal infectious disease. In many 
developing countries, attempts to control the spread of infection rely solely on 
identification and treatment of those with active disease, ignoring subclinical 
infection. However, in developed countries, large efforts are also expended to 
identify and give prophylactic drugs to people with latent tuberculosis 
infection. Until recently, the 100-year-old tuberculin skin test (Mantoux) has 
been the only available diagnostic test for latent tuberculosis infection, 
despite its many well-known limitations. Advances in scientific knowledge have 
led to the development of tests for tuberculosis that measure the production of 
interferon-gamma by T-cells stimulated in vitro with Mycobacterium 
tuberculosis-specific antigens. These interferon-gamma tests are highly specific 
and unaffected by prior Bacille Calmette-Guérin vaccination or immune reactivity 
to most atypical mycobacteria. They are more sensitive than the tuberculin skin 
test in detecting people with active tuberculosis, and their results correlate 
more closely with M. tuberculosis exposure risk factors than the tuberculin skin 
test in people likely to have latent tuberculosis infection. Science has caught 
up with one of the oldest diagnostic tests still in use worldwide, and the 
adoption of new, tuberculosis-specific interferon-gamma-based tests should move 
us one step closer to better control of this insidious pathogen.