大肠肿瘤的多基因，多位点突变的进行性积累对其发生、发展及演进起着十分重要的作用，该过程涉及众多原癌基因如ｒａｓ的激活和抑癌基因Ｐ~５３的灭活~［１］。本文采用ＰＣＲ－ＳＳＣＰ技术对２５例大肠肿瘤组织中的Ｐ~５３基因５～８外显子及Ｋｉ，Ｎ－ｒａｓ基因第１外显子 The progressive accumulation of multi-gene and multi-site mutations in colorectal tumors plays an important role in its occurrence, development and progression. This process involves the activation of numerous proto-oncogenes such as ras and the inactivation of the tumor suppressor gene P~53~ [1]. In this study, PCR-SSCP technique was used to analyze the exons 5-8 of P53 gene and exon 1 of Ki,N-ras gene in 25 cases of colorectal tumors.