We determined almost complete small-subunit ribosomal DNA sequences of 50 reference strains belonging to the genera Corynebacterium, Rhodococcus, and Gordona and compared these sequences with previously published sequences. Three phylogenetic methods (the neighbor-joining, maximum-likelihood, and maximum-parsimony methods), as well as a bootstrap analysis, were used to assess the robustness of each topology which we obtained. The results of comparative phylogenetic analyses confirmed that the genera Corynebacterium, Dietzia, Gordona, Mycobacterium, Nocardia, Tsukamurella, and Turicella form a monophyletic taxon within the phylum containing the high-G+C-content gram-positive bacteria. The genus Corynebacterium appeared to be a monophyletic unit whose members could be divided into four major clusters. The validity of the genus Turicella is doubtful since members of this genus clearly belong to the genus Corynebacterium. The variability of chemotaxonomic characteristics within the genus Corynebacterium suggests that small-subunit ribosomal DNA sequence analysis is probably the most straightforward method for confirming that a bacterium belongs to this genus.