CDC eugonic oxidizer group 2 (EO-2) is a group of unclassified gram-negative bacterial strains isolated from various human sources. As determined by biochemical tests and analyses of fatty acid compositions, these organisms form a homogeneous group that appears to be distinct from but related to other Paracoccus species. Molecular studies were performed on a set of 13 EO-2 strains from various clinical sources and geographic locations in the United States and Canada to determine their relationship to the Paracoccus genus. Control strains were Paracoccus denitrificans ATCC 17741(T), P. versutus ATCC 25364(T), P. aminophilus ATCC 49673(T), P. solventivorans ATCC 700252(T), and Psychrobacter immobilis ATCC 43116(T), which are phenotypically similar to EO-2. Nearly complete (1,500-base) 16S rRNA gene sequencing of eight EO-2 strains showed a high level of sequence similarity (>99.3%) within the group, and a BLAST search of GenBank placed the EO-2 cluster in close proximity to Paracoccus species (95 to 97% similarity). DNA-DNA hybridization studies of 13 of the EO-2 strains showed all to be related at the species level, with >70% relatedness under stringent conditions and a divergence within the group of less than 2%. None of the Paracoccus control strains hybridized at >54% with any of the EO-2 strains. These results indicate that EO-2 represents a new Paracoccus species, the first isolated from human clinical specimens. A new species, Paracoccus yeeii, is proposed for the EO-2 strains. The type strain of P. yeeii is CDCG1212 (ATCC BAA-599 and CCUG 46822), isolated in Pennsylvania from dialysate of a 77-year-old male with peritonitis.