A method for the in vitro diagnosis of colorectal cancer by determining the presence of the protein disulfide isomerase tumor marker in a biological sample taken from a patient suspected of having colorectal cancer using at least one anti-PDI monoclonal antibody directed against a PDI epitope chosen from the epitopes of sequence SEQ ID NO: 1, SEQ ID NO: 2 with an aromatic amino acid having a three-dimensional structure similar to that of PDI, and SEQ ID NO: 3.
