p53 protein accumulation, thought to be caused by p53 gene mutation, is closely related to poor prognosis of patients with certain types of carcinomas. The progression of esophageal squamous cell carcinoma (SCC) is also strongly suspected to depend on the p53 tumor suppressor gene. Formalin-fixed, paraffin-embedded sections were taken from 25 patients who underwent esophagectomy for SCC. Fourteen patients had no preoperative therapy (control group), while the other 11 patients received preoperative radiotherapy (radiation group). There was no difference in pathological TNM classification between the two groups. These sections were examined by immunostaining with monoclonal antibody PAb 1801 to determine the accumulation of p53 protein, and apoptotic frequency was determined by TdT mediated dUTP-biotin nick end-labeling (TUNEL). In the control group, well to moderately differentiated cases showed a significantly higher AI (apoptotic index which is the number of apoptotic cells among 1000 cancer cells. %0) (51.7+/-83.4) than poorly differentiated cases (AI=1.3+/-1.0) (P<0.05). Similar results were obtained in the radiation group. The former group included 4 cases of p53 grade 4 (p53 protein detected in over 70% of the tumor cells), and the latter included 2. Few apoptotic cells were observed in any of 6 tumor tissues. In each patient, tumor cells with accumulated p53 protein were very rare to be apoptotic. On the other hand, apoptosis was observed in tumor cells without p53 protein accumulation. Spontaneous apoptosis in esophageal SCC can be induced more easily in differentiated than in poorly differentiated cases. This tendency may be enhanced by preoperative radiotherapy. Extensive p53 protein may suppress apoptotic induction in esophageal squamous cell carcinomas.