Values from an ELISA for evaluating the immune response induced by a commercial vaccine against fowlpox virus and the lesion at the site of inoculation (i.e., swelling of the skin or a pox where the vaccine was applied) were compared. The ELISA was carried out with an antigen prepared by precipitation of a cell culture–propagated virus suspension with ammonium sulfate and concentration by centrifugation. A 0.1 M acetate buffer (pH 5) was used as the sensitizing solution for maximum specific binding of the antigen to the microplate plastic well. Four experiments were conducted where the birds were bled once a week before and after vaccination and then were examined simultaneously for evidence of “takes.” This study showed that there is a relationship between the ELISA values to the fowlpox vaccine that are considered positive and the presence of postvaccination lesions.