Sera from 35 individuals with suspected allergies to inhaled flour were screened for the presence of immunoglobulin E (IgE) specific for wheat-flour proteins. Sera from nine asthmatic bakers with high wheat RAST scores were selected for further study with the aim of purifying the allergen(s) involved in bakers' asthma and related conditions. However, each of the different techniques applied--ion exchange chromatography, preparative isoelectric focusing and the electrophoretic transfer, or 'Western blotting' technique, showed that serum IgE from different individuals have markedly different specificities and bind to numerous wheat proteins. When three purified wheat proteins were tested--wheat germ agglutinin; a fraction purified using a concanavalin-A affinity column and a putative trypsin inhibitor--all were identified as allergens for some but not all of the allergic bakers.