To evaluate the influence of intraoperative irradiation on the healing of jejunal annastomosis, an experimental study was undertaken using a total of 150 rats. The bursting pressure of the normal jejunum was obtained in gropu I. Group II was subjected to resection and anastomosis, and group III was irradiated on the anastomosed jejunum with a single dose of 1,000 rads. Healing process was evaluated by measuring bursting pressure of the anastomosed jejunum on each postoperative day from 2nd to 14th, and on 21th day. Bursting pressure was tested by inflating the loop of gut with water, and bursting sites were observed. The results obtained are summarized as follows : 1. The bursting pressure of the anastomosed jejunum retained normal strength by the 7th postoperative day in the nonirradiated group, whereas by the 11th postoperative day in the irradiated group. 2. Irradiation caused delay in the healing of anastomosis of the jejunum until the 10th postoperative day ; but after then there was no significant difference in bursting pressure between both groups. 3. In the jejunal segments with subnormal strength, bursting occurred exclusively at the non-anastomotic site in both groups; Bursting started along the mesenteric border in the non-irradiated group, whereas rupture usually occurred on the antimesenteric border in the irradiated group. In the jejunal segments with subnormal strength, bursting usually started on the mesenteric border of the anastomotic site in both groups. The results indicate that intraoperative irradiation with a single dose of 1,000 rads causes no harmful effect on the healing of anastomosis of the jejunum in rats. Therefore, this study suggests the possibility of more effective clinical application of intraoperative irradiation.