Tuberculosis (TB) is a major global health problem. TB is the current leading cause of death due to an identifiable infectious agent worldwide. One of the highest priorities for tuberculosis control programs is to shorten anti-TB treatment while maintaining its effectiveness. Current 6-month short course chemotherapy regimens are over 95% effective for the treatment of tuberculosis when fully administered. Six months is a long time, however, and patients frequently discontinue anti-TB treatment once their symptoms have improved. The duration of standard short course chemotherapy is one of the major obstacles to its successful application and poses substantial challenges to programs with respect to patient adherence, program resource needs, and logistical requirements for directly observed therapy. The primary objective of this study is to assess the efficacy of shortening anti-TB treatment to 4 months in human immunodeficiency virus (HIV)-non-infected adults with drug-susceptible, non-cavitary pulmonary tuberculosis who convert their sputum culture to negative after 2 months of treatment. Secondary objectives of this study include: comparing pre-treatment sputum bacillary load in patients with and without cavitary disease; compare time after inoculation of BACTEC or Mycobacteria growth indicator tube (MGIT) liquid culture media until positive with semi-quantitative sputum acid fast bacteria (AFB) smear and culture on solid media as measures of pre-treatment sputum bacillary load; and determining the influence of immunologic characteristics of subjects pre-treatment, during treatment and at the end of therapy on rate of bacillary clearance and risk for relapse. A total of 758 HIV-non-infected adults, male or female, 18-60 years of age, with newly diagnosed initial episodes of sputum AFB smear-positive or -negative, culture-positive, non-cavitary, drug-susceptible pulmonary TB who are sputum culture negative after 2 months of anti-TB treatment will be randomly assigned to complete a total of 4 or 6 months of anti-TB therapy. The experimental regimen will include a total of 4 months of anti-TB treatment [2 months of daily isoniazid (INH), rifampicin, pyrazinamide and ethambutol followed by 2 months of daily INH and rifampicin]. The comparative regimen will include a total of 6 months standard short course anti-TB chemotherapy (2 months of daily INH, rifampicin, pyrazinamide and ethambutol followed by 4 months of daily INH and rifampicin). Subjects will be involved in study related procedures for approximately 30 months after beginning the initial anti-TB treatment.