[en] Using highly sensitive radioimmunoassay kits, the level was examined of carcinoembryonic antigen in a group of 154 patients with suspect colorectal carcinoma. In 67% of 112 patients with histologically confirmed diagnosis of colorectal carcinoma an increased production of carcinoembryonic antigen was recoreded which was highly dependent on the stage of disease and partially on the histological type of the tumor. However, an increased level of carcinoembryonic antigen was found also in 35% of those patients in whom malignity failed to be established. This false positivity, along with the lack of carcinoembryonic antigen production in the 33% of patients with histologically confirmed diagnosis of colorectal carcinoma clearly indicate that examination of the level of this antigen cannot be used as an indicator of the presence of colorectal carcinoma in the organism without knowledge of the clinical condition of the patients as well as the results of other examinations. (author)