The tumor marker test CA19-9 is based on monoclonal antibody to colonic carcinoma cell lines. In this study, the utility of the tumor marker in the diagnosis of pancreatic carcinoma was evaluated. CA19-9 is strongly expressed in most tissue specimens from pancreatic carcinomas. However, this antigen is also found in normal pancreas and specimens from chronic pancreatitis. CA19-9 is released into the circulation, and was found in increased concentrations (greater than 37 U/ml) in 87% of the patients with pancreatic carcinoma (N = 145), as compared with only 13% in the group of patients with benign diseases (N = 1081) and 29% of those with extrapancreatic malignancies (N = 691). The preoperatively raised CA19-9 concentration in patients with stage I of pancreatic carcinoma decreased after curative resection of the carcinoma to values within normal range. However, in no CA19-9 estimation following a palliative surgical intervention of stage III and IV patients or in cases of inoperable carcinomas was a serum concentration of less than 37 U/ml recorded. The mean survival rate of stage I patients was 29 months, whereas it was only 6 months for stage III, IV and patients with inoperable carcinomas.