To study the in vivo interaction between lentinan-stimulated alveolar macrophages and Mycobacterium tuberculosis were used rats intranasally infected with 2 x 10(8) CFU. Before infection animals were treated intranasally with lentinan at a dose of 1 mg/kg (administrated three times at 2 days periods). Samples of broncho-alveolar lavage fluid were obtained from rats at different intervals -3, 24 and 72 h after infection. The process of phagocytosis in vivo was observed by light and electron microscopy, as well as acid phosphatase cytochemistry methods. Bactericidal activity of alveolar macrophages following the same intranasal installation of lentinan was assessed by in vitro "killing" ability test against M. tuberculosis. Nitrite production by lentinan activated alveolar macrophages was measured 24 h after ex vivo culture of these cells. It was demonstrated that lentinan induces high level of alveolar macrophage activation manifested through enhanced bactericidal effect against M. tuberculosis, which correlates with the induction of reactive nitrogen intermediates, increased activity of lysosomal enzymes (acid phosphatase), and with effective phagolysosomal fusion followed by destruction of Mycobacteria.