A living vaccine, the bacille Calmette Guérin (BCG) strain of Mycobacterium tuberculosis bovis, has been administered in a single postoperative intrapleural dose as a controlled equivalent of postoperative empyema in 38 patients following pulmonary resection for lung cancer. This form of regional immunotherapy is reasonably well tolerated if the vaccine is given in a limited dose and if a follow-up course of isoniazid (INH) is administered. In this report, the technical details of this new therapeutic program are reviewed. The preliminary findings in a randomized prospective clinical train of the technique indicate that patients with Stage I lung cancer are significantly benefitted by the treatment. Patients with more advanced disease are unimproved by this form of therapy.