The phenotypic and functional properties of T cells were evaluated in patients with tuberculin anergy and a possible role of anergic T cells in the development of immune deficiency in pulmonary tuberculosis (PT) was studied. The profound decrease (more than 50%) depressed T-cell proliferation in PPD-stimulated cultures was shown to be recorded in 44% (59/134) patients with PT. PPD hyporesponsiveness was associated with the low proliferation of anti-CD3 and SEB-stimulated proliferation of a healthy donor's mononuclear cells evidencing the enlargement of anergic T cells with a suppressive activity in PT. A PPD-stimulated response in healthy donors was under the negative control of CG25-positive cells. In the PPD-anergic patients, there was a significant increase in CD4+CD25+ T cells that were inversely correlated with the PPD-induced proliferative response. The development of tuberculin anergy was more pronounced in patients with drug resistance. The intensity of a PPD-stimulated response in patients with tuberculin anergy may be restored in the presence of exogenous interleukin-2.