In a prospective study (N = 566) we investigated the tumour associated carbohydrate-protein CA 242, focusing on the question whether CA 242 (CaNAG, Sweden) expression in carcinoma patients is distinctly higher than in benign disorders, especially when compared to CA 19-9 (EIA Roche Germany). A second point of interest was if CA 242 is expressed to a higher extent in early stages of colorectal cancer than CEA (MEIA Abbott, USA) and CA 19-9 are, and third its behavior in pancreatic and lung cancer. We found CA 242 values comparable in healthy individuals and benign gastrointestinal disorders, thus CA 19-9 remains the marker of first choice for pancreatic cancer and CEA for colorectal cancer. CA 242 shows no advantage in lung cancer as compared to the established markers (CEA, CYFRA 21-1 (EIA Roche Germany) and NSE (EIA Hoffmann LaRoche, Switzerland) and no clearly higher expression in early colorectal cancer. Overall, the combination of CEA and CA 242 shows the best sensitivity in colorectal cancer.