Basophil-bound IgE was measured by quantitative immunofluorescence microscopy in atopic subjects and in healthy controls. A correlation was found between IgE serum level and basophil-bound IgE. The basophils from the atopic patients, both from those with a low and those with an increased serum IgE, showed a significantly higher fluorescence intensity than the basophils from the respective controls. Our results indicate that both atopy and the IgE level of the serum determine the amount of basophil-bound IgE.