Detection of specific IgE by the radioallergosorbent test (RAST) which uses labelled antibody can be hampered by the presence of antibodies other than IgE but with the same specificity and may limit usefulness of the RAST for diagnosis of IgE-mediated milk allergy in infancy when high titres of cow's milk protein-specific IgG antibodies are known to be present. This can be avoided by using a system employing labelled antigen, such as the enzyme-linked immunosorbent assay (ELISA) described here, where IgE in the test serum is immunoadsorbed to anti-human IgE coated to microtitre plates. Biotinylated antigen, in this case cow's milk proteins, binds to specific IgE and the reaction is revealed colorimetrically by adding horseradish peroxidase (HRP)-avidin conjugate.