Nasopharyngeal carcinoma(NPC) is a tumor of an increasing incidence in Korea. Multiple etiologies such as gentic factors, dietary factors, and Epstein-Barr virus(EBV) infection, have been suggested by a number of epidemiological studies performed mainly among the Chinese population where this disease record the highest prevalence. Alteration in the structure of p53 gene represent one of the most common genetic changes associated with human cancer. Recent investigations show that mutation of the p53 gene is a very rare event in NPC. We have analyzed 33 cases of NPCs(10 squamous cell carcinomas and 23 undifferentiated carcinoma) for EBER 1 and overexpression of p53. p53 overexpression was detected in 4 out of 10(40%) cases of squamous cell NPCs and in 7 out of 23(30.4%) cases of undifferentiated NPCs I where the rate of EBERI positivity showed 60% and 87% repectively. Regardless of the histopathological diagnosis, EBV positive cases showed 29.6% of p53 overexpression whereas EBV negative cases showed 50% overexpression. The above results suggest that different mechanisms are involved in the carcinogenesis of undifferentiated NPCs and squamous cell NPCs, we think that mutation of p53 tumor suppresser gene and EBV infection are included in these mechanisms. The authors conclude that EBV infection does not seem to cintribute to the immunoreactivity of p53 proteins.