We have established a solid-phase binding inhibition radioimmunoassay for the detection of colorectal carcinoma-specific antigens in tissue culture supernatants of human colorectal carcinoma cell lines and in serum and urine of colorectal carcinoma patients. Using the [3H]glucosamine-labeled cell membrane glycolipid antigen and colorectal carcinoma-specific monoclonal antibodies in this assay, we have been able to detect several human colorectal carcinoma membrane-specific antigens that are released from the cell membrane into tissue culture supernatants, and an antigen detected by antibodies 1116-NS-19-9 and 1116-NS-52a that is found only in the serum and urine of cancer patients.