BACKGROUND: Mutations of the tumor suppressor gene p53 cause subsequent cellular accumulation of p53 gene product and a specific immunologic response. Detection of circulating antibodies against p53 protein has been evaluated for a tumor marker or prognostic factor for several cancers including those of the breast, stomach, ovary and lung. METHODS: Serum samples from 74 colorectal cancer patients were obtained preoperatively and anti-p53 antibody was measured by enzyme immunoassay (Anti-P53 ELISA II: PharmaCell, France). Carcinoembryonic antigen (CEA) and Carbohydrate antigen (CA) 19-9 were measured in parallel. Tissue p53 protein expression was examined by immunohistochemical staining. RESULTS: Anti-p53 antibodies were positive in the serum from 34% (25/74) of patients, but normal controls were all negative. Anti-p53 antibodies were significantly associated with p53 protein overexpression. CEA and CA19-9 were detected in 38% and 11%, respectively. There was no correlation among anti-p53 antibody, CEA and CA19-9. No differences were found between the anti-p53 antibody positive and negative groups in the following parameters: tumor site, histologic grades, Dukes stages, margin invasion, vessel invasion, lymph node and distant metastasis, and survival duration. CONCLUSIONS: The measurement of serum anti-p53 antibody is not suitable for preoperative markers of prognostic significance, but can be used as a simple serological marker for detection of p53 alteration. There should be more studies of the serum p53 antibody as a possible marker for postoperative monitoring in colorectal cancer.