BACKGROUND: IFN-gamma is known to activate mononuclear phagocytes and to mediate host defense mechanism against some intracellular microorganisms, but litfle is known about anti-mycobacterial activity and mechanism of IFN-gamma in human. In this study, we investigated the role of IFN-gamma in the pathogenesis of tuberculosis by observing the effect of IFN-gamma on the phagocytosis of M.tuberculosis(MTB) and on the production of TNF-alpha by human pulmonary alveolar macrophage. METHOD: Pulmonary alveolar macrophage(PAM) were prepared with adhesion purification method from bronchoalveolar lavage fluid obtained from 8 persons without active lung lesion and cultured(1 x 106cells/ml) with MTB(3 x 107 bacteria/ml) with or without IFN-gamma(300U/ml), LPS(0.5ug/ml) and autologous serum(10%). After 2 hours, the percentage of PAM-phagocytosed MTh was counted after AFB staining(modified Kynion method). TNF-alpha production by PAM stimulated by IFN-gamma(300U/ml), MTB(1 x l06bacteria/ml) and LPS(0.5ug/ml) for 24hours was measured in culture supernatant using ELISA method. The degree of phagocytosis of MTh by PAM stimulated with IFN-gamma(300U/ml) and LPS(0.5ug/ml) for 24hours was also investigated. RESULTS: IFN-gamma did not influence the phagocytosis of MTB by PAM(percentage of PAM-phagocytosed MTB: control: 22.1+/- 4.9, IFN-gamma: 20.3+/- 5.3) and did not increase TNF-alpha production by PAM(controfl 21+/-38pg/ml, IFN-gamma : 87+/-106pg/ml), and the degree of phagocytosis of MTh by PAM pre-stimulated with IFN-gamma for 24 hours, was not increased (controL 24.5+/-9.5, IFN-gamma : 23.4+/-10.1). CONCLUSION: IFN-gamma does not influence on the phagocytosis of MTB and TNF-alpha production by PAM.