AbstractThe clinical efficacy of intraoperative radiation therapy (IORT) and the changes of immunological parameters were investigated. Nine patients with unresectable pancreatic cancer were treated with IORT (2,500‐3,500 cGy) and the changes of various immunological parameters were compared with those in 11 patients with advanced cancer who received external beam irradiation therapy (XRT), 2,500‐3,500 cGy. After IORT, 71% of patients obtained pain relief, two of the nine patients showed a partial response, and the serum CA 19‐9 level decreased in six patients. However, the median survival was only 210 days. Natural killer activity, lymphokine‐activated killer activity, and interferon γ‐activated killer activity were not inhibited by IORT, and phytohemagglutinin‐induced blastogenesis was actually augmented after IORT, whereas all these parameters were inhibited by XRT. Thus, it is suggested that IORT may augment or at least stabilize systemic antitu