A new method is described for the quantitative detection of IgE antibodies, based on IgE capture with a specific antibody, reaction with liquid-biotinylated allergens and biotinylated anti-IgE and immunoenzymatic development of the reaction (reverse enzyme allergosorbent test). Using a reference system based on the World Health Organization IgE International standard, this method determines total IgE in the range 2–100kU/L and specific IgE in the range 0.2–100 kU/L, from which the specific/total ratio, called ‘specific IgE density’, can be calculated. This procedure has been applied to the study of specific IgE in 23 sera from patients polysensitized to pollen and mite allergens: 11 with asthma and 12 with rhinitis. The sensitivity and reproducibility of the method were evaluted. Sera from asthmatic patients showed higher cumulative levels of specific IgE (mean density 57.7%) than sera from rhinitic patients (mean density 32.6%). The clinical significance of specific IgE density in patients with multiple sensitizations is discussed.