A variety of studies have suggested that depressed individuals may have increased medical morbidity and mortality and that depression is associated with neuroendocrine changes. Furthermore, the applicant has found that lymphocyte function is suppressed in grieving subjects. The proposed research will test the hypothesis suggested by these observations that depression is associated with altered immune function. Preliminary studies comparing hospitalized depressives and controls are consistent with this hypothesis. Depressed subjects will be studied immunologically soon after admission to the hospital for treatment of their depression. The lymphocyte stimulation responses of these acutely depressed patients will be compared to those of a group of control subjects. In order to control for possible effects of hospitalization, immune function in a group of ambulatory subjects with depressive disorders and a group of hospitalized individuals with schizophrenia will be compared to groups of normal age and sex matched controls. In addition, the depressed subjects will be followed longitudinally to determine if altered lymphocyte responsivity is in function of the state of clinical depression.