Exocrine proteins contained in human pancreatic juice were separated in two dimensions using isoelectric focusing and sodium dodecyl sulfate gel electrophoresis. Nineteen discrete proteins were found. Fifteen of these were identified by actual or potential enzyme activity and include three forms of trypsinogen, two forms each of procarboxypeptidase A, procarboxypeptidase B, proelastase, and colipase, and one form each for amylase, lipase, chymotrypsinogen, and prophospholipase A2. Lipase and four unidentified proteins were found to contain carbohydrate by the periodic acid Schiff staining method. Each pancreatic protein was characterized by isoelectric point and molecular weight. Proteins were quantitated according to relative mass, as measured by the incorporation of a mixture of 15 3H-amino acids into secretory proteins contained in tissue slices, and according to the distribution of Coomassie blue R stain among proteins contained in pancreatic juice, as determined by two-dimensional gel scanning and computer analysis. The second form of pancreatic procarboxypeptidase B (IEPn6.7) was present in only 4 of 10 subjects tested. Trypsinogens 1 and 3 were covalently labeled with 35SO4. Trypsin derived from trypsinogen 2 showed no inhibition with soybean trypsin inhibitor or Trasylol.