Background : Mutations in the p53 gene are the most frecjuent genetic alterations found in human cancers to date. Bvidense suggests that wild-type p53 is a tumor suppressor protein, crucial for the negative regulative of cell cycling, and requiring loss of function mutations for tumorigenesis. Objective : Our purposr is to investigate the expression pattern of the p53 protein in the squamous cell carcinomas(SCCs) of the human skin. Methods : We studied p53 protein expression, using DO7 mnoclonal antibody immunohi-stochemistry, in 29 SCCs of the skin. Also, we compared the p53 expression depending upon with or without a history of UV exposure. Results : p53 immunoreactivity was observed in 48% (14 of 29) of SCCs and was not seen in normal skin. In 56% (16/29) SCCs the tumors were developed on UV-light exposure area. SCCs were divided on histopatal biological criteria in to three categories, well, moderately, or poorly differentiated. Although no significant differenie in the prevalence of p53 immunoreactivity was obierved between these groups, positive, strong staining was observed more frequently in poorly differentiated than in well-differe: treated tumors. Conclusion : Accumulat,i,on of p53 protein, suggestive in nessary cases of p53 gene mutation and hence loss of tumors upperesor function, may play a role in the tumorigenesis of SCCs. (Kor J Derrnatol 1994; 32(6): 9555-961)