Sera from 58 patients with suspected extrinsic allergic alveolitis (EAA) were tested in parallel by the double diffusion test and the "enzyme-linked immunosorbent assay (ELISA)" using 10 different antigen solutions (extracts from thermophilic actinomycetes, various mycetes, pigeon serum, pigeon droppings and the wheat weevil sitophilus granarius). The ELISA technique was more sensitive than the double diffusion test in detecting antibodies to the panel of antigens used. However, by using several antigen dilutions the number of sera positive sera with the double diffusion test increased and an overall correlation of 93.1% with the ELISA was achieved. The results of the study are discussed with regard to the advantages and disadvantages of both test systems for the in vitro diagnosis of EAA.