We determined the following immune parameters in drug-free, major depressed patients and in age- and sex-matched healthy controls: the number and percentage of interleukin-2 receptor (IL-2R) bearing cells (CD25+, anti-TAC), serum circulating levels of soluble (s)IL-2Rs, the pre- and postdexamethasone phytohemagglutinin (PHA)-induced accumulation of sIL-2Rs in culture supernatant, and the number of T helper (CD4+) and T suppressor (CD8+) cells. In comparison with normal volunteers, patients with major depression had a higher number and percentage of CD25+ cells, higher concentrations of serum circulating sIL-2Rs, higher supernatant sIL-2Rs after stimulation with PHA, and a higher number of CD4+ cells. The CD4+/CD8+ ratio and the number of CD4+ cells were significantly and positively related to the number of cells expressing the CD25+ antigen. These results may indicate that depressed patients display an increased number of T cells in an early phase of activation.