A Complement Fixation Test (CFT) was developed for the diagnosis of Erysipelas infections. The results of that work were compared with those of the Growth Inhibition Test (GIT), and they showed that the CFT test was very useful to determine whether an animal had been vaccinated or was still suffering from the disease. The CFT is as reliable as the GIT in detecting recent as well as chronic infections, but its value is limited where animals are examined for their response to a vaccination.