The IgE response to inhaled dust of pancreatic powder was studied with sera from two employees of a pharmacy. IgE from both sera was directed against both porcine and bovine trypsin preparations. The major IgE-binding structures had an isoelectric point in the pH 8 to 9 range. The molecular weight of the IgE-binding structures was different for both patients. In one patient, most IgE was directed against a 28 to 30 kd structure, whereas the second patient had IgE directed against components with a molecular weight of 35 and 45 kd, respectively.