A total of 26 patients with depression and 20 healthy subjects were studied. Measures of apoptosis of peripheral blood lymphocytes and serum cortisol concentrations were determined. A significant increase in lymphocyte apoptosis was found in patients with depression, resulting in an increase in the proportion of lymphocytes expressing the FAS receptor; cells with morphological signs characteristic of apoptosis (nuclear condensation, vacuolization) were also seen. Changes in cellular immunity were observed on the background of clinical depressive symptomatology, with decreases in the total numbers of T-lymphocytes (CD3(+)), T-helpers (CD4(+)), and natural killer cells (CD16(+)) as compared with numbers in healthy subjects. Serum cortisol levels were elevated. Correlation analysis revealed an interaction between high cortisol levels and decreases in T-helper cells (CD4(+)) and increases in apoptosis receptor expression in patients with depressive disorder.