The diagnostic value of the tumor-associated antigens Ca 19-9 and Ca 12-5 was tested in 130 subjects (38 healthy controls, 37 carcinomas of the pancreas, 23 chronic pancreatitis, 23 extrapancreatic gastrointestinal cancers, 9 endocrine pancreatic tumors). Ca 19-9 levels above 37 U/ml were obtained in 67.6% and Ca 12-5 levels above 39 U/ml in 45.9% of carcinomas of the pancreas, 4.3 and 8.7%, respectively, of chronic pancreatis, 21.7 and 17.4% of extrapancreatic gastrointestinal tumors, and 0 and 11.1% of endocrine pancreatic tumors and in none of the healthy controls. Results of preoperative determination of Ca 19-9 and Ca 12-5 gave a sensitivity of 67.6 and 45.9%, a specificity of 91.8 and 90.9%, a predictive value of a positive test of 80.6 and 70.8%. When elevation of both antigens was required, sensitivity decreased to 32.4% but specificity rose to 97.3%. All but one of the pancreatic cancer patients were at stage 3 and 4. The only patient with pancreatic cancer in stage 1 had normal levels of both markers. Ca 19-9 and Ca 12-5, whether alone or associated, represent a good diagnostic test for differentiating pancreatic cancer from chronic pancreatitis. Due to the low sensitivity of both markers, the tests are of limited value when any other diagnostic evidence of pancreatic cancer is absent.