A radioimmune method based on detection of IgE antibodies (RAST) has been used for allergen quantitation, both as a direct test and as an inhibition test. Commercially available allergen extracts from birch pollen, timothy pollen and horse dandruff were studied. Variations of the allergen concentration up to a thousandfold were found between some extracts and these differences were confirmed by the results obtained with the chopped human lung test and in provocation tests. The use of RAST for estimation of allergen concentrations seems to be of great value, since the method combines easy performance with high capacity and independence of allergic patients as test objects. The same set of test sera can be used for several years, ensuring standardized conditions.