Menaquinones were the only isoprenoid quinones found in 40 strains representing I9 species of Actinomadura, Microbispora rosea, Microtctrasporu glauca, Microtctrasporu niwoulbu, Nocardiopsis dassoncillei and Streptomjices somuliensis. The Nocardiopsis dassonrillei st rains had a characteristic profile consisting of major amounts of di-, tetra-, hexa-and octahydromenaquinones with ten isoprene units and were thereby distinguished from all of the other test strains which contained complex mixtures of hydrogenated menaquinones with nine isoprene units. The latter strains were divided into three groups based upon the predominant isoprenologue detected : (1 . n izwmlhu con t a i n e d tetra h y d rog enated menaquinones with nine isoprene units. The results show that menaquinone profiles are of value both in generic and sub-generic classifications of Actinomudura. They also suggest that some species of Microbispora and Microfetruspora are closely related to Actinomadura, a result in line with other trends in the taxonomy of these organisms.