Abstract
SUMMARY: Complement-fixation tests were used to compare strains of Mycoplasma mycoides var. mycoides (5 strains), M. mycoides var. capri (5 strains) and M. laidlawii of bovine genital origin (3 strains). Strains of M. mycoides and M. capri showed cross-reactions of about 25% identity, but strains of M. laidlawii appeared to be antigenically distinct. The results, measured in terms of the amounts of complement fixed, are shown graphically and discussed in relation to the diagnosis of contagious bovine pleuropneumonia.