In 2000, the U.S. had over 16,000 cases of infectious tuberculosis and an estimated 10-15 million latent cases. Despite prolonged treatment regimens with significant side effects, reports of drug resistant TB in 43 states, and an estimated $345 million market opportunity, few new drugs to treat TB are in development. FASgen's SBIR Phase I goal is to choose a lead anti-tuberculosis candidate from 6 molecules active in vitro against Mycobacterium tuberculosis. ? ? Phase I specific aims are: 1) resupply candidate compounds and determine purity and chemical and biological stability; 2) determine minimum inhibitory concentrations (MICs) against a panel of mycobacteria in vitro; 3) determine in vitro cytotoxicities (lC50s) against Vero cells; 4) determine maximum tolerated dose (MTD) and dose limiting toxicity in mice for compounds with selectivity index (MTD/IC50) >10; 5) test the best compound in a murine inhalation model of TB; 6) verify that the MTD is not substantially different in immunocompromised (beige) mice; 7) test whether the best anti-tuberculosis compound is also active against M. avium in an immunocompromised mouse model; 8) repeat/confirm efficacy in animal models. ? ? In SBIR phase II, the lead compound will undergo safety/toxicology testing in animals and Phase I/Il safety and Phase II efficacy testing in man, most likely against multidrug resistant TB.