Our phylogenetic analysis based on 16S ribosomal DNA (rDNA) sequences and chemotaxonomic analyses showed that Nocardioides simplex ATCC 13260, ATCC 19565, and ATCC 19566 are more closely related to the genus Rhodococcus, especially Rhodococcus erythropolis, than to the genus Nocardioides. N. simplex ATCC 13260 and N. simplex ATCC 19565 and ATCC 19566 exhibited levels of 16S rDNA similarity of 99.4 and 100%, respectively, to R. erythropolis DSM 43066T. Strains ATCC 13260, ATCC 19565, and ATCC 19566 had mesodiaminopimelic acid in their peptidoglycan and MK-8(H2) as their predominant menaquinone. These three strains produced cellular fatty acid patterns similar to those of R. erythropolis strains rather than those of Nocardioides species. Therefore, N. simplex ATCC 13260, ATCC 19565, and ATCC 19566 should be reclassified as strains of R. erythropolis Gray and Thornton 1928.