Organisms with the typical characteristics of mycoplasmas were isolated from the tracheae of buzzards, saker falcons, and griffon vultures. All isolates obtained from the same bird species appeared to be serologically identical and distinct from the isolates obtained from the other two bird species and from the previously described Mycoplasma, Entomoplasma, Mesoplasma, and Acholeplasma species. The results of an indirect immunofluorescence test, a growth inhibition test, and an immunobinding assay showed that the isolates belong to three new species, for which the names Mycoplasma buteonis (seven strains obtained from buzzards), Mycoplasma falconis (six strains obtained from saker falcons), and Mycoplasma gypis (eight strains obtained from griffon vultures) are proposed. M. buteonis ferments glucose, does not hydrolyze arginine or urea, reduces tetrazolium chloride and potassium tellurite anaerobically, does not produce films and spots, and does not possess phosphatase activity. M. falconis does not ferment glucose, hydrolyzes arginine but not urea, reduces tetrazolium chloride and potassium tellurite anaerobically, does not produce films and spots, and does not possess phosphatase activity. M. gypis does not ferment glucose, hydrolyzes arginine but not urea, reduces tetrazolium chloride and potassium tellurite aerobically and anaerobically, produces films and spots, and possesses phosphatase activity. The three new species lyse avian, bovine, equine, human, ovine, porcine, rabbit, and guinea pig erythrocytes, but do not adsorb these erythrocytes. The type strain of M. buteonis is Bb/T2g (= ATCC 51371), the type strain of M. falconis is H/T1 (= ATCC 51372), and the type strain of M. gypis is B1/T1 (= ATCC 51370).