In the last few years, an increase in the incidence of malignant tumours of the large bowel and the rectum has been observed in all advanced countries. Intensive search is therefore going on for biochemical and immunochemical markers which would help early diagnosis and monitoring of this disease. The most frequently used markers in colorectal cancer are CEA, CSi, CRP, CA 19-9 and sialic acid. The present study points out the possibility and advantage of using lysozyme determination in serum as another marker in patients with colorectal cancer.