Immunologic function as measured by lymphocyte response to phytohemagglutinin (PHA) mitogen was evaluated in 8 psychiatric inpatients. All were less than 45 years of age and had a DSM-III diagnosis of major depression. When patient's immunologic responses were compared with healthy age- and sex-matched controls, a significant increase in PHA mitogen stimulation was observed in the depressed group. Further, a significantly greater variance in PHA response was observed in the patients compared with controls. The literature on depression and immunity is reviewed and the clinical implications of our findings are discussed.