Objective: To investigate the p53 overexpression and its correlation with neoplastic cell mitosis and apoptosis in 43 nasopharyngeal carcinomas (NPCs). Methods: Forty-three pretreated NPC biopsy samples were randomly collected in the year 1997 for this study. p53 overexpression was detected by LSAB immunohistochemistry using DO-7 primary antibody. Mitotic figures were counted on H&E stained slides, and apoptotic cells on TUNEL-stained slides by use of in-situ cell death detection kit. Both of mitotic and apoptotic cells were quantitated by cell numbers per one high power field (5(40) averagely in terms of mitotic index (MI) and TUNEL index (TI), respectively. To compare the mean MIs of two groups categorized by different percentages of positive p53 positive cells found in NPC specimens was taken for the purpose of designating the criterion of p53 overexpression. And then, the correlation of p53 overexpression with MI and TI was made by statistical analysis. Results: Because statistically significant difference appeared at the criterion of 20%, the p53 overexpression of NPC was defined as≥20% of positive cells found. The p53 overexpression thus could be detected in 37 out of 43 NPCs, reaching 86.05% (37/43). The mean MI (1.87(1.78/HPF) of 37 NPCs with p53 overexpression was significantly higher than that (0.76(0.63/HPF) of 6 NPCs without p53 overexpression, the P value being <0.05. However, there was no statistical difference between the mean TI (24.50(26.66/ HPF) of 37 NPCs with p53 overexpression and TI (23.17(25.30/HPF) of 6 NPCs without p53 overexpression. Conclusions: p53 overexpression of NPC could be designated by ≥20% of positive neoplastic cells found in pretreated NPC specimens, and the rate of which reached 86.05% (37/43). The overexpressed p53 could enhance cell proliferative activity in pretreated NPCs represented by increasing of MI, but showed no effect on neoplastic cell apoptosis. Objective: To investigate the p53 overexpression and its correlation with neoplastic cell mitosis and apoptosis in 43 nasopharyngeal carcinomas (NPCs). Methods: Forty-three pretreated NPC biopsy samples were randomly collected in the year 1997 for this study. P53 overexpression was detected by LSAB immunohistochemistry using DO-7 primary antibody. Mitotic figures were counted on H & E stained slides, and apoptotic cells on TUNEL-stained slides by use of in-situ cell death detection kit. Both of mitotic and apoptotic cells were quantitated by cell numbers per one high To compare the mean MIs of two groups categorized by different percentages of positive p53 positive cells found in NPC specimens was for the the purpose of designating the criterion of p53 overexpression. And then, the correlation of p53 overexpression with MI and TI was made by statistical analysis. Results: Because statistica The p53 overexpression of NPC was defined as ≧ 20% of positive cells found. The p53 overexpression was could be detected in 37 out of 43 NPCs, reaching 86.05% (37/43). The mean MI (1.87 (1.78 / HPF) of 37 NPCs with p53 overexpression was significantly higher than that (0.76 (0.63 / HPF) of 6 NPCs without p53 overexpression, the P value being <0.05. However, there was no statistical difference between the mean TI (24.50 (26.66 / HPF) of 37 NPCs with p53 overexpression and TI (23.17 (25.30 / HPF) of 6 NPCs without p53 overexpression. Conclusions: p53 overexpression of NPC could be designated by ≥20% of positive neoplastic cells found in pretreated NPC specimens, and the rate of which reached 86.05% (37/43). The overexpressed p53 could enhance cell proliferative activity in pretreated NPCs represented by increasing of MI, but showed no effect on neoplastic cell apoptosis.