Multi-drug-resistant tuberculosis (MDR-TB) has emerged as an obstacle to the control of tuberculosis. Recent data however, suggest that interferon-(IFN)-g and IFN-a may improve disease evolution in subjects affected with pulmonary tuberculosis caused by multi-resistant (IFN-g) and sensitive (IFN-a) strains. The mechanisms involved are not known, even though it has been reported that IFN-g-secreting CD4+ Th cells may possess antitubercular effects. In addition, IFN-a can induce IFN-g secretion by CD4+ Th cells, and both types of IFN may stimulate macrophage activities. The aim of this study was to explore the possibility that aerosolized IFN-a, administered concomitantly with conventional antitubercular chemotherapy, may improve the course of pulmonary tuberculosis. After six months of directly observed therapy (DOT), seven patients who were non-responders to a second line antitubercular therapy were given an IFN-a aerosol (3 MU, three times a week) for two months as adjunctive therapy. All strains were resistant to at least two first-line drugs. After IFN-a administration, the patients were followed up for a further six months with the same DOT. Sputum samples were collected monthly during the study period, with the exception of the IFN-a administration period, when the observations were performed weekly. High resolution computed tomography (HRCT) chest scans were performed before and after IFN-a inhalations. The analysis of the results showed that the mean number of Mycobacterium tuberculosis (Mt) had remained statistically unchanged (p= 0.80) during the first 6 months of DOT. During the following 2 months of IFN-a administration, 5 patients became negative (p= 0.02). After the end of treatment a progressive increase in Mt number was observed (p= 0.02). Sputum cultures remained positive for all patients throughout the study period, although a significant decrease (p= 0.02) in the colony number per culture was observed after adjunctive treatment with IFN-a. After stopping administration of IFN-a, a significant increase (p= 0.03) in the colony number per culture was noted as well as in Mt numbers. HRCT scans were slightly improved in all patients. These preliminary data suggest that aerosolized IFN-a may be a promising adjunctive therapy for patients with MDR-TB. Optimal doses and schedules however, require further studies.