For a better understanding of the molecular mechanism leading to intraductal precipitation of proteins in primary chronic calcifying pancreatitis in man, we studied the composition of normal and pathological human pancreatic juice by immunotechniques. We found an increased level of serum proteins in pathological juices: 12.47% of total proteins compared to 1.8% in normal ones; albumin is 8.16% of the total proteins, IgG 2.84%, IgA 0.83% and IgM 0.91%. Transferrin and alpha 2-macroglobulin are present, but were not estimated. The albumin/IgA and albumin/IgG ratios favour the hypothesis of a local synthesis of these immunoglobulins as was shown in normal juice. The cross adsorption of antisera against pancreatic juice showed the presence in the pathological juice of a normal molecule in much higher concentration. The role of these proteins in precipitation is discussed.