Parameters of immune activation/differentiation were studied in a group of newly diagnosed HIV- and HIV+ pulmonary tuberculosis (TB) patients. Compared with controls, HLA-DR expression on both CD4 and CD8 T cells from the HIV- TB patients was approximately doubled; HLA-DR on T cells from the HIV+ group was tripled. The monocytes from both groups of patients expressed abnormally high levels of the Fc gamma receptors I and III. Serum levels of tumour necrosis factor-alpha (TNF-alpha), neopterin and beta 2-microglobulin were increased in HIV- and even more so in HIV+ TB patients. The expression of HLA-DR on T cell subsets and of Fc gamma R on monocytes correlated with each other, but not with serum activation markers. This pattern of non-specific activation during TB infection may be associated with enhanced susceptibility to HIV infection.