PURPOSE:The aim of this study was to compare carcinoembryonic antigen levels with detection of messenger ribonucleic acid coding for the tumor‐associated antigen L6 in patients with colorectal cancer. Not only are carcinoembryonic antigens expressed by the corresponding tumor cell, but the messenger ribonucleic acid of tumor‐associated antigens, in contrast, is produced exclusively by viable tumor cells.METHODS:L6 messenger ribonucleic acid was determined by reverse‐transcription polymerase chain reaction. Carcinoembryonic antigen was measured by the enzyme‐linked immunosorbent assay technique, with a cutoff value of 40 &mgr;g/l. Blood serum was sampled from 187 patients with colorectal cancer. Statistical significance was calculated with the McNemar chi‐squared test.RESULTS:Preoperatively, 79 percent of patients in all stages were positive for L6 messenger ribonucleic acid, whereas only 35 percent had elevated carcinoembryonic antigen titers (P< 0.001). In Dukes A tumors, 84.9 percent of patients were positive for L6 messenger ribonucleic acid, whereas carcinoembryonic antigen was elevated in only 16.9 percent of patients. Only in Dukes D tumors did the enzyme‐linked immunosorbent assay for carcinoembryonic antigen exhibit the same sensitivity as reverse‐transcription polymerase chain reaction for L6 messenger ribonucleic acid. Recurrence was detected significantly earlier by reverse‐transcription polymerase chain reaction for L6 messenger ribonucleic acid than by enzyme‐linked immunosorbent assay for carcinoembryonic antigen.CONCLUSION:L6 is more sensitive and precise than carcinoembryonic antigen in diagnosing and monitoring colorectal cancer.