&NA;Twenty‐nine of 31 patients bearing resectable colorectal cancers had elevated levels of serum Tennessee antigen in comparison with only eight of 31 patients for carcinoembryonic antigen. This high detection rate is, however, of limited value since the level of serum. Tennessee antigen is not specific for the presence of malignancy. There appeared to be no relationship between the level of preoperative serum Tennessee antigen and subsequent prognosis. Furthermore, in only nine of 31 patients did the serum Tennessee antigen level fall after removal of all macroscopic cancer. There also appeared to be no relationship between the level of serum TennaGen at three months after resection and subsequent prognosis. These findings are in contrast, to estimations of serum carcinoembryonic antigen.