The effect of fermentation by Lactobacilliand of proteolytic hydrolysis of whole milk on the IgE binding ability of ?-lactoglobulin was studied using an ELISA inhibition assay. Sera from nine adult milk allergic patients were tested. The individual sera showed a similar inhibition pattern in the changes during fermentation and proteolysis. The degradation of ?-lactoglobulin was studied with liquid chromatography. In general, fermentation with Lactobacilli gave little effect on IgE binding, even though chromatography data showed a gradual degradation of ?-lactoglobulin. Proteolysis with trypsin, however, gave extensive degradation of ?-lactoglobulin and strongly decreased IgE binding. In addition, we measured the inhibition pattern of ?-lactoglobulin in various selected commercially available fermented milk products. These showed an IgE binding capacity similar to that of nonfermented high pasteurized milk. © 2005 American Chemical Society.