Human pancreatic fluid obtained from 2 subjects, each with a traumatic pancreatic fistula, contained detectable levels of IgG, IgA, IgM, IdD, and IgE. Although the mean IgG/IgA ratio for 10 random specimens was 1.63, the relative concentration was estimated to be less than unity when extreme values were eliminated. The molecular weight of IgA in pancreatic fluid was found to be comparable to that of the IgA molecule in serum. The absence of secretory component in pancreatic IgA provides further evidence that pancreatic IgA and serum IgA are similar. Serial determinations of the immunoglobulins stored at 4 degrees C showed a progressive decrease of all immunoglobulins, the order of stability being IgG approximately equal to IgA larger than IgM approximately equal to IgD. The demonstrated proteolytic activity in the specimens could account for the immunoglobulin decay and for the variable detection of IgM and IgD in pancreatic-fluid specimens.