Chronic ethanol ingestion predisposes to tuberculosis and bacterial pneumonia. Mycobacterium avium complex (MAC) organisms cause bacteremia in patients with AIDS. Cultured human monocyte-derived macrophages and murine Kupffer cells were exposed to 10-100 micrograms/dl ethanol; significantly greater intracellular growth of MAC strains 100 (serovar 8) and 101 (serovar 1) occurred in ethanol-treated cells than in controls (range, 58% +/- 7%-70% +/- 5%; P less than .05 for 50 and 100 micrograms/dl ethanol vs. control). Both cell types, when treated with 10(3) units/ml recombinant tumor necrosis factor (TNF) or 10(2) units/ml granulocyte-macrophage colony-stimulating factor (GM-CSF) in the presence of 10-100 micrograms/dl ethanol, killed significantly fewer MAC than controls (49% +/- 12% decrease for GM-CSF and 57% +/- 16% for TNF; P less than .05 for all comparisons). C57BL black mice infected intravenously with MAC strain 101 were given ethanol as 4% of total calories daily; after 21 days they had greater numbers of MAC in blood, liver, and spleen than controls. Ethanol's effects on the interaction between the host and MAC favor progressive infection.