Crossed immunoelectrophoresis was applied to purify Y. enterocolitica common antigen by precipitation with monospecific rabbit anti- P. aeruginosa CA antibody. Monoclonal antibodies against Y. enterocolitica CA were then raised by immunization of mice with these immunoprecipitates. This method provides the possibility of producing a panel of anti-CA monoclonal antibodies from a large number of bacterial species.