Abstract: Nineteen multibacillary (LL or BL type) leprosy patients were treated with Isobutylpiperazinyl rifamycin(R-76-1)150 mg daily for 6 to 18 months with a definite therapeutic effect as shown by the clinical assessments, skin, smears and histologic studies. Tlie improvement was more marked daring the first 6-month period than the second and third 6-month periods-with unknown reason.Mouse foot pad inoculation with serial skin biopsy specimens had been obtained from 10 patients of this group.