The relationships between postoperative immunodepression and duration of general anesthesia, volume of blood transfusions, cortico-steroid administrations and amount of surgical trauma have ben studied, in cancer patients undergoing radical operations. Postoperative depression of cellular immunity, assayed by the lymphocyte blastogenic response to phytohemagglutinin, was significantly correlated with the amount of surgical trauma and did not correlate with blood transfusions and corticosteroid administrations, nor with the duration of anesthesia.