Correlations between infiltration of Langerhans cells (ILC) in tumor tissues and radiation curability were investigated in 449 patients with cervical cancer treated with radiation alone, including 390 squamous cell carcinomas and 59 adenocarcinomas. No significant difference in prognosis was noted in stage I, II, and IV squamous cell carcinomas between positive and negative ILC. However, in the patients with stage III squamous cell carcinoma, a significantly better survival was observed for patients with ILC than for those without, 10 year survival rates being 78% vs. 54%, P < 0.01. In adenocarcinoma, the patients with ILC also showed significantly better survival than those without ILC, the 10 years survival rates being 45% vs. 25%, P < 0.025. An analysis of failure patterns following radiation treatment demonstrated that the favorable prognosis in patients with ILC in squamous cell carcinoma was due to improvement of local control rates and somewhat lower metastatic rates, whereas in adenocarcinoma it was only due to better local control rate. The ILC was significantly associated with T-cell infiltration in tumor tissues. The immunological stimulation with Sizofiran in 20 patients led to an augmentation of ILC in tumor tissues. The present study suggests that the ILC in cancer tissues improves local response to radiation treatment partly by T-cell mediated anti-tumor activity.