[en] The haemolytic antibody isotope release (HAIR) assay quantitates antibody production by splenic antibody-producing cells by lysis of chromium-51-labelled sheep red blood cells. The amount of antibody quantitated by the HAIR assay directly correlates with the number of antibody-producing cells measured by a conventional plaque assay. The HAIR assay is an easy, sensitive, and reproducible technique that is especially useful when large numbers of animals are required for testing. (author)