[en] Endoscopic and histological effects and perianal dermal side effects after high-dose-rate intraluminal brachytherapy (HDRIBT) using ⁶⁰Co for preoperative irradiation were assessed in thirty-five patients with low-lying rectal cancers. In more than half of the patients irradiated with 30 Gy or more, marked effective change was observed under endoscopy. In the histological assessment, while the resected lesions irradiated with 16-20 Gy showed no effective change, 68.8%, 75.0%, and 76.9% respectively, of those in the groups given 30 Gy, 40-60 Gy, and 80 Gy showed marked destruction. While 23. 1% of the patients irradiated with 80 Gy developed severe perianal dermal lesions requiring surgical removal of the anus, 18.8% of the 30 Gy group and 25% of the 40-60 Gy group suffered from dermal side effects which were mild and reversible. Consequently, it has been concluded that the proper regimen for preoperative HDRIBT for rectal cancer was 30 Gy followed by surgery within two weeks. During the follow up period from 35 to 70 months, one patient (2.9%) who received 16 Gy HDRIBT developed local recurrence within 3 years after resection, and the other one developed hepatic metastasis. The 3-year local recurrence rate after resection for lower rectal cancer in the previous series at our department was 19.6%. We, therefore, concluded that HDRIBT was a promising adjuvant therapy for rectal cancer. (author)