The diagnostic value of pyruvate-kinase type tumor M2 (Tumor M2-PK) has been investigated in different tumors, and showed interesting results in cases of renal cancer, pancreatic cancer, lung cancer and some cases of gastric cancer. In this study we investigated EDTA-plasma of 68 patients with gastrointestinal cancer, 22 patients with inflammatory bowel disease (IBD) and 60 healthy controls. Sensitivity of Tumor M2-PK was 70.6% for all GI-tumors, that of CA19-9 was 55.4% and that of CEA was 53.3%. In pancreatic cancer CA19-9 showed the best sensitivity. In oesophageal/gastric cancer Tumor M2-PK was most sensitive and in colorectal cancer CEA and Tumor M2-PK showed the best results. The specificity of Tumor M2-PK was 90-96, 7%. In IBD some individuals showed elevated Tumor M2-PK levels but there was no correlation to CRP or to the clinical activity score. The results indicated that Tumor M2-PK might be a valuable marker in gastrointestinal cancer.