In the elderly, an impairment of the immune system could lead to increased incidence of infectious, neoplastic and autoimmune diseases; on the other hand, depression, which is the most common psychiatric problem in aged people, seems to be linked with alterations in immunological function. Thirteen institutionalized elderly subjects were studied to investigate the relationship between depression and immunological parameters. These subjects were selected as "healthy" according to the SENIEUR-EURAGE protocol and they belonged to a population already evaluated by our group--one year before--for psychological, endocrinological and immunological parameters. The lymphocyte mitotic response to PHA was greatly diminished in aged subjects, when compared to the adult controls. Depressed elderly showed impaired immunological function as compared with nondepressed ones, either "in vitro" or "in vivo". Lymphocyte stimulation with phytohemagglutinin (PHA), T cell growth factor (TCGF) production (induced by stimulation with PHA) and cutaneous delayed hypersensitivity (CDH) were reduced in depressed aged subjects. As far as lymphocyte proliferation with PHA in the whole group were concerned, no differences were found comparing the present results with those obtained in a former study. Although it is difficult to understand the significance of the immune imbalance associated with depression in the elderly, our results suggest that psychological status could influence the immunological functions in old people.