Inflammatory cells in lymph nodes of eighteen patients suffering from culture-proven tuberculous lymphadenitis were examined by histological and immunohistochemical techniques. Ten patients suffered from symptomatic HIV-infection and eight patients were immunocompetent individuals without HIV-1 serology. Characteristic granulomas with or without caseation were observed in eight immunocompetent and four HIV-1-infected patients with less marked lymphopenia of CD4 positive peripheral blood lymphocytes. No epitheloid cell formation was present in lymph nodes of HIV1-infected patients with more severe depression of CD4 positive peripheral blood lymphocyte count. Foamy macrophages were found instead of these cells. While many cells--predominantly lymphocytes--express CD25 (IL-2 receptor) in cases with typical epitheloid granulomas there is no such CD25 expression in cases without any epitheloid cell formation. This result suggest that T cell function is necessary for epitheloid granuloma formation in human tuberculosis. The phenotype of macrophages underwent progressive changes parallel to decreasing numbers of CD4 positive peripheral blood lymphocytes. Foamy macrophages in Mycobacterium avium-intracellulare infection represented an end-stage phenotype. They were positive for S100 protein and they did not express lysozyme, alpha-1-anti-chymotrypsin, L1 antigen (Mac387) and CD4, whereas positivity for HLA-DR, CD68 and Ki-M8 was preserved. In situ immunohistochemical demonstration of IFN-alpha, IFN-beta, TNF-alpha, IL-1 and IL-6 revealed that foamy cells in M. tuberculosis infection were highly active effector cells. They contained higher concentrations of the examined cytokines than epitheloid cells in the lesions of HIV+ and HIV-patients. Corresponding to these findings the histological proof of acid-fast bacilli was generally not successful in typical HIV-associated tuberculosis. The foamy appearance may result from the lipid-rich cell membranes of destroyed acid-fast bacilli. In contrast acid-fast bacilli-packed foamy macrophages in AIDS patients with M. avium-intracellulare (MAI) infection did not produce any of the examined cytokines.