We have evaluated the clinical utility of tumor-associated trypsin inhibitor (TATI) in colorectal cancer and compared it with carcinoembryonic antigen (CEA), the classical marker for this disease. We measured the serum levels of these markers in 53 patients with colorectal carcinoma before and after surgery. CEA was found to have greater sensitivity than TATI in this disease. The TATI concentrations did not correlate as well as CEA with the presence or absence of metastasis and with the course of the disease after surgery. The use of TATI together with CEA for detection or follow up of colorectal cancer does not seem to be useful because a significant increase of positivity is not obtained as compared with determination of CEA alone.