Although effective medications to treat and even prevent Tuberculosis (TB) have been available for over 40 years, TB remains the most important infectious cause of mortality among adults in the world. One of the cornerstones of control of this disease is detection and treatment of infection – while it is still latent, or dormant. Nine months of Isoniazid (INH) is highly effective to treat latent infection, and so is considered the standard therapy. However, this therapy is often unsuccessful, because the long duration reduces completion rates, and increases cost, and it is associated with serious, even fatal side effects. An alternate regiment, of four months Rifampin has been recommended by authoritative agencies as an alternative, but there is surprisingly little data regarding the safety and efficacy of this regimen. We propose a randomized trial to compare the safety and costs of this regimen with the standard of 9 months INH, having completed a preliminary trial which demonstrated that the 4RIF regimen had significantly better completion rates. If the safety of 4RIF can be shown to be as as good, or better, than 9INH, then we will continue with a larger scale trial to compare the efficacy of the two regimens in preventing future active cases of TB among persons with latent TB infection