We studied clinical significance of serum SPan-1 antigen, which is human pancreatic cancer associated antigen, in hepatobiliary and pancreatic diseases employing newly developed kit. The sensitivity of serum SPan-1 antigen levels for pancreatic cancer, gallbladder carcinoma, hepatocellular carcinoma, bile duct cancer were 90.9%, 77.8%, 60.7%, 60.0% respectively. No correlation was found between serum SPan-1 antigen levels and total bilirubin levels. SPan-1 positivity in patients with hepatic disease including hepatocellular carcinoma was rather high, but there were few cases more than 100 U/ml. The mechanism of the elevated level was supposed to be release of the antigen from bile-duct epithelium, and this must be taken into consideration at diagnosis referred to serum SPan-1 antigen level.