The aim of this study was to investigate the adjuvant effects of interferon-gamma (IFN-gamma) inhalation therapy for six months in the treatment of refractory multidrug-resistant pulmonary tuberculosis (MDR-TB). Aerosolized IFN-gamma was given to six MDRTB patients with persistent positive smears and cultures despite long-term medical treatment. The patients received aerosolized two million international units of IFN-gamma three times a week for 6 months while they continued on identical antituberculous chemotherapy. Before IFN-gamma inhalation therapy, the patients received a median of 6.5 (range, 4 to 7) antituberculous drugs for median duration of 29 months (range,7 to 76). After IFN-gamma inhalation therapy, sputum smears remained persistently positive in all patients throughout the study period. Sputum cultures were transiently negative at the 4th month in two patients, but became positive again at the end of 6 months of IFN-gamma therapy. Five patients had radiological improvement including three patients who showed a decrease in the size of the cavitary lesions. Resectional surgery could be performed in one patient in whom substantial clinical and radiological improvement was noted after IFN-gamma inhalation therapy. These results suggest that IFN-gamma inhalation therapy may be effective for some cases of refractory MDR-TB who are otherwise not responding to conventional therapy.