Allergen extracts contain a wide variety of allergenic determinants and the sensitization of allergic subjects is extremely heterogeneous. Specific immunotherapy is usually performed with multiple component extracts and it is therefore important to determine whether this treatment may elicit the onset of newly developed IgE sensitivities. By means of nitrocellulose immunoblotting technique, the IgE sensitivities of 20 patients were characterized before and after specific immunotherapy. Ten patients had a rush immunotherapy with a standardized orchard grass pollen extract and ten others underwent a rush immunotherapy with a 6-grass pollen allergoid. The allergenic profiles of the patients before and after immunotherapy were qualitatively similar. In some patients an increase of orchard grass pollen-specific IgE was observed and the allergenic profile was quantitatively different. These results suggest that rush immunotherapy with either an aqueous non-modified extract or an allergoid does not elicit the onset of new IgE sensitivities. Multicomponent allergenic extracts may therefore be used in the treatment of patients.