In a prospective study of 15 spouses of women with advanced breast carcinoma, lymphocyte stimulation responses to phytohemagglutinin, concanavalin A, and pokeweed mitogen were significantly suppressed during the first two months following the death of a spouse compared with prebereavement levels. A highly significant suppression was seen as early as one month after bereavement. No differences were found in total lymphocyte or B- or T-cell numbers. An intermediate level of mitogen responsivity was found during the four- to 14-month period after bereavement. Suppressed immunity following the death of a spouse may be related to the increased morbidity and mortality associated with bereavement.