In 1971, rifampin was approved for treatment of pulmonary tuberculosis and asymptomatic carriers of Neisseria meningitidis. At present, the approved indications remain the same. However, rifampin in conjunction with at least one other antituberculous drug may be of great value in therapy of extrapulmonary tuberculosis and infections due to other susceptible mycobacteria. In addition, results of clinical trials in leprosy have been highly encouraging. Rifampin appears to induce light chain proteinuria in a majority of patients and has been implicated in suppression of both humoral and cell-mediated immune responses. However, these effects appear to have been of little consequence to treated patients. A variety of possibly immunologically mediated reactions to rifampin has been closely associated with irregular administration of the drug. These reactions and hepatic toxcity may be preventable in many patients. Rifampin or one of its congeners, alone or in combination with other antibiotics, may prove useful in treatment of various infectious, and possibly malignant, diseases.