The amplified enzyme-linked immunosorbent assay (a-ELISA) has been successfully applied to the measurement of allergen-specific IgE and IgG antibodies. Data presented indicate a high positive correlation among measurements of IgE-specific antibodies to ragweed antigen E using the a-ELISA, RAST and radiometric assay of Zeiss. Similarly, a high correlation between allergen-specific IgG antibodies measured by the a-ELISA and Farr assay was also observed. Data presented indicate that the measurement of serum IgE antibodies in the linear region of the ELISA titration plot is unaffected by competition with IgG antibodies. The assay is sensitive, reliable, and without risk to laboratory personnel. It is capable of measuring both IgE and IgG antibodies in patients using the same assay system.