New blood tests have become available to detect either latent or active tuberculosis. These tests - which according to the CDC can replace the tuberculin skin test - measure the production of gamma-interferon (a cytokine) by peripheral lymphocytes (white cells) when exposed to antigens which are highly specific of mycobacterium tuberculosis (the bacteria responsible for tuberculosis). Our hypothesis was that the production of gamma-interferon would be much higher at the beginning of treatment than at the end, and that decline in gamma-interferon secretion could be an indicator of clinical response to treatment.