Chemotherapeutic agents such as 5-FU, pyrimidine analogue and irradiation were well known to induce stomatitis as a complication. It was considered that stomatitis might be induced by disturbance of the turnover of epithelium in the oral cavity. There have been a few reports studying the turnover of the tongue epithelium performed by autoradiography. The purpose of this study was immunohistochemical observations of turnover of the tongue epithelium using anti-BrdU antibody. The materials of this experiment consisted of 30 ICR adult mice. Using immunohistochemical staining method of Bromodeoxyuridine, we observed the turnover of tongue epithelium at 1 hour. 5 hours, 6 days, 8 days and 10 days after injection of BrdU and labeling index at 1 hour was calculated. The results were as follows ; 1) In the control, there was no labeled element in the tongue epithelium. 2) The labeling index of the 1 hour after BrdU injection was 9.5±2.7% in average. 3) 5 hours after BrdU injection, BrdU-labeled elements were concentrated at the basal layer of the epithelium. 4) 6 days after BrdU injection, BrdU-labeled elements were located in the upper part of epithelium, 5) 8 days after BrdU injection, BrdU-labeled elements were still located in the epithelium, but labeling elements decreased. 6) 10 days after BrdU injection, labeling elements were not observed in the epithelium. The above results suggest that average labeling index after 1 hour of BrdU injection is 9.5±2.7% and the turnover of the tongue epithelium in normal mice may be within.