A group of 10 patients with recently diagnosed pulmonary TB were studied and compared to 10 bacillus Calmette Guérin (BCG) immunized healthy individuals. Cellular immune mechanisms were explored in vitro utilizing fresh and precultured peripheral blood mononuclear cells exposed to PHA, PPD, and recall antigens (SK/SD and CA). Proliferative assays were also carried out in the presence of either each patient's serum (autologous serum) or cocultured with CD3+ depleted adherent cells. Serum measurements of soluble interleukin-2 (IL-2) receptor and synthesis of IL-2 generated by mononuclear cells stimulated with PPD and SK/SD were also performed. Patient sera were able to inhibit autologous as well as allogeneic cell responses, and a significant adherent cell suppressive effect was observed. As a whole the group of patients showed decreased blast transformation to PPD, preserved proliferative responses to other recall antigens, and a low PPD-induced generation of IL-2. Furthermore, as possible evidence of preactivated T cells, these patients demonstrated high soluble IL-2 receptor serum levels. Early compromise of specific cell-mediated immunity, including IL-2 abnormalities, may be of significance in newly diagnosed pulmonary TB.