The name Enterobacter cowanii sp. nov. is proposed for a group of organisms referred to as NIH Group 42. Members of this species are Gram-negative, motile rods conforming to the definition of the family Enterobacteriaceae. The DNA relatedness of nine strains of NIH Group 42 to the proposed type strain of this species averaged 85% at 70 degreesC, whereas the relatedness to other species within the family Enterobacteriaceae was less than 38%. Because the DNA relatedness (5-38%) is closer to species of the genus Enterobacter than to other species of the family, the members of NIH Group 42 were placed in the genus Enterobacter. The majority of strains of E. cowanii were isolated from clinical specimens. A culture of the type strain (888-76) has been deposited in the Japan Collection of Microorganisms as JCM 10956.