The purpose of this research is to further study the tuberculosis (TB) vaccine, Bacillus Calmette Guérin (BCG). The goal of this study is to evaluate whether the BCG vaccine is more effective in preventing TB in adults if it is given after 6 months of treatment with a widely used anti-TB drug, isoniazid (INH). Participants will include 82 healthy, tuberculin skin test positive (TST+), HIV-uninfected, male and female volunteers, aged 18-40 years. The study will be conducted in Worcester, South Africa. Subjects will be assigned by chance to 1 of 2 possible treatment groups. Group 1 will receive 6 months of oral INH treatment followed by intradermal (administered into the skin) BCG revaccination and one year of follow-up. Group 2 will be observed for 7 months which will be followed by intradermal BCG revaccination and another 6 months of follow-up. Then 6 months of INH treatment will be given. Participants will be involved in study procedures for about to 22 months.