OBJECTIVE: To study the relationship between metastasis of colon cancer and the mutation of p53 gene. METHODS: PCR-SSCP was used to analyse exon 5-9 of the p53 gene in 73 cases of Dukes C human primary cancer and 40 cases of matched lymph node metastasis. RESULTS: Mutations were identified in 27 of 73 primary cancers (37%) and 19 of 40 lymph node metastasis (47.5%) with the overall incidence of p53 mutation being 44%. In 21 of 40 cases in which both primary and metastatic cancers were analysed by SSCP, we found no p53 mutations in both lesions. While the same exon and exactly the same mutated band pattern could be seen both in primary and metastatic cancers in another 12 cases (30%). In addition, the agreement of p53 mutation status in primary cancer to the lymph node metastases was lost in the remaining 7 cases (17.5%). All of the 7 cases were confirmed to have base substitution mutations by DNA direct sequencing. In 5 of 7 individuals, the point mutations were detected only in lymph node metastases but not in the primary cancers and in 2 of 7 cases, two exons were found to have mutations in lymph node metastases while only one or no mutation was identified in the primary cancers. CONCLUSION: Most p53 mutations occurred before metastasis and p53 mutations persist throughout the final stage of the progression and metastasis in colon cancer. Furthermore, the metastasis of colon cancer is accompanied by the emergence of new mutation in p53 gene or metastasis is selected against the p53 mutation, which suggests that the mutations in p53 gene may be related to the metastasis of colon cancer