We measured the concentration of hepatocyte growth factor (HGF) in the sera of 138 patients with gastrointestinal cancer. The mean value and positive rate for this protein (assuming 0.4 ng/ml as the cut-off value) were 0.29 ng/ml (11.4%) in healthy donors (n=44), 0.90 ng/ml(70.8%) in esophageal cancer (n=24), 0.39 ng/ml (33.3%) in gastric cancer (n=39), and 0.40 ng/ml (42.7%) in colorectal cancer (n=75). Thus, the mean values of the esophageal and colorectal cancer group were significantly higher than that of healthy donors. There was a tendency for elevated mean value of serum HGF in the sera of patients with distant metastases, compared to those with no such evidence, i.e., 1.36:0.77 ng/ml in esophageal cancer, 0.69:0.30 ng/ml in gastric cancer, and 0.66:0.37 ng/ml in colorectal cancer. This difference was statistically significant in gastric and colorectal cancer. These findings suggest that serum HGF is useful as a tumor marker with a close correlation to the metastatic state of gastrointestinal cancer.