Carcinoembryonic antigen (CEA) is one of the better-studied oncodevelopmental antigens to which numerous monoclonal antibodies (MoAbs) have been generated. Many of these MoAbs have been recently grouped (Gold classification) according to their epitope recognition. The present study was designed to immunocharacterize various MoAbs, each representative of the five Gold groups, on colorectal cancers and normal tissues using semiquantitative immunohistochemistry. Sensitivity, based on the number of colorectal cancer cases (n = 100) with positive reaction (> 5% cells), was greater with Gold groups 1 and 2 (93% each) than with groups 3, 4, and 5 (78%, 83%, and 87%, respectively). The intensity of the strain also correlated with the Gold groups, with 24%, 20%, and 18% of cancer cases displaying weak or negative staining (0 or 1+) when reacted with MoAbs from groups 3, 4, and 5, respectively, versus 6% and 12% with Gold 1 and 2 antibodies. Cross-reactivity of the anti-CEA antibodies with CEA-related molecules was found to be significant with Gold 5 antibody, which stained most of the normal lung, liver, stomach, and intestinal tissues tested. Strong staining also was seen in granulocytes when they were reacted with Gold 4 and 5 antibodies. The other antibodies showed much less and variable cross-reactivity with normal tissues, with a not statistically significant advantage for Gold 1 antibodies. In addition to lower sensitivity in CEA detection, Gold 3 to 5 MoAbs were less specific due to cross-reaction with one or more of the CEA-related macromolecules expressed by normal tissues. Based on these results and given the broad clinical applications of anti-CEA MoAbs, it is essential to characterize each MoAb to be used for clinical purposes in order to avoid interpretation errors of potential relevance resulting from poor sensitivity/specificity. The use of antibodies that recognize the epitope of group 1 or 2 is recommended to maximize sensitivity and specificity for CEA detection.