CA 19-9 and CEA serum levels were determined before and 7 days after surgery in 140 patients with gastrointestinal adenocarcinoma, and in 70 patients with gastrointestinal non neoplastic diseases. CA 19-9 test was shown to be positive in 37.9% of colorectal cancer, in 32.6% of gastric cancer and in 77.8% of pancreatic cancer. CA 19-9 test was also shown to be more sensitive for colonic cancer with respect to rectal cancer (40.9% vs. 23.5%). CA 19-9 test is more sensitive and specific than CEA. In particular, the reported results suggest the clinical value of CA 19-9 test in the diagnosis of pancreatic adenocarcinoma and as a suitable parameter in the follow-up of gastrointestinal cancer.