Mycoplasma arginini Barile et al. 1968 and Mycoplasma leonis Heyward et al. 1969 are regarded as synonyms on the basis of comparisons of the original species descriptions and of the serological and biochemical characteristics of authentic strains, including the type strains, of each of the organisms. According to the rules of nomenclature, the correct name of the species formed by the union of these two taxa is M. arginini Barile et al., which name has priority over M. leonis Heyward et al.