Patients with culture-positive pulmonary tuberculosis were allocated at random into two groups for a three-phase regimen in original course chemotherapy. The first group was given rifampicin (RMP) plus isoniazid (INH) plus ethambutol until sensitivity tests were completed, then RMP plus INH until culture conversion, thereafter INH alone for four months. The second group received the same drugs until obtaining culture conversion, thereafter IHN alone for a period lasting two years after onset of chemotherapy. One hundred sixty-eight patients were available for the final assessment after a five-year follow-up after culture conversion. Two bacteriologic relapses occurred among the two-year scheme patients, none in the short-course patients.