The 16S rRNA primary structures of Eubacterium suis DSM 20639T (T = type strain) and Bifidobacterium bifidum DSM 20456T were determined by sequencing in vitro amplified rDNA. Sequence comparisons indicated that B. bifidum is moderately related to representatives of the genera Actinomyces and Mobiluncus. The closest relative of E. suis is Actinomyces pyogenes. E. suis and A. pyogenes are more closely related phylogenetically to one another than to the other Actinomyces species that have been investigated by using comparative 16S rRNA analysis. Therefore, we propose that E. suis should be transferred to the genus Actinomyces as Actinomyces suis comb. nov.