Reverse transcriptase sequencing of 16S ribosomal ribonucleic acids of some representatives of the genus Rhodococcus were performed in an attempt to clarify their intra- and inter-generic relationships. The results indicate that the genus Rhodococcus as presently constituted is phylogenetically heterogeneous. On the basis of the 16S ribosomal-RNA sequence and earlier chemical data it is proposed that the genus Gordona (Tsukamura) be revived to accommodate those rhodococcal species containing relatively long-chain mycolic acids (48 to 66 carbon atoms) and MK-9(H₂) as the predominant menaquinone type.