The CA(carbohydrate antigen)19-9 is complex protein that can be used as an important marker which aids the clinical diagnosis and prognosis of various pancreaticobiliary tumors. However, it was also reported that there were some CA19-9 positive patients with benign disease as using RIA method. The purpose of this study is to evaluate the clinical usefulness of serum level of CA19-9 with RIA(radioimmuno assay), CIA(chemiluminescence immuno assay), and conventional liver function tests. The correlation between CIA and RIA in CA19-9 of pancreatobiliary disease was 0.9833(P<0.01). Also, the correlations between CIA and RIA in CA19-9 of benign and malignant pancreaticobiliary tumor patients was 0.8714(P<0.01) and 0.9727(P<0.01) respectively. The correlation between CA19-9 and ALP was 0.5140(P<0.01) and CEA was 0.3385(P<0.05) as using CIA. The measurement of serum CA19-9 levels by CIA method may be useful in differentiating patients with malignant disease from those with benign disease in pancreaticobiliary tumors.