Serum levels of tissue polypeptide antigen specific (TPS), a cytokeratin 18 marker, were determined and compared with serum levels of carcinoembryonic antigen (CEA) in 45 patients with colon adenocarcinoma and in 34 patients with benign diseases (adenomatous polyps and ulcerative colitis) at the time of diagnosis. In colon carcinoma patients 58% had an elevated TPS level (cut-off 100 U/l) and 53% had an elevated CEA level (cut-off 3.0 ng/ml). The sensitivity of the cytokeratin marker TPS was related to the stage of the disease. Significant correlation was observed between TPS and Dukes stages in colon cancer patients and the highest TPS values were achieved in Dukes stage D. The combined use of the two markers increased the sensitivity to 82% compared with the use of only one. Simultaneous raise of both serum markers TPS and CEA was observed in 36% of cases. In the majority of the patients with adenomatous polyps and ulcerative colitis the serum TPS and CEA levels were below the upper reference limit. However the initial high levels in some patients could be considered as a prognostic indicator for identifying a group of patients with increased risk of cancer development. No significant correlation was observed between serum TPS and CEA concentrations in individual patients with benign diseases.