A halophilic gram-negative rod was isolated from blood and cerebrospinal fluid collected from a 70-year-old male having no known contact with seafood or salt water. Positive biochemical tests included oxidase, sensitivity to 0/129, O-nitrophenyl-beta-D-galactopyranoside, lysine decarboxylase and fermentation of glucose, salicin, n-inositol, sucrose, L-mannose, L-arabinose, and arbutin. Negative tests included indole, ornithine decarboxylase, arginine dihydrolase fermentation of lactose, and production of gelatinase and urease. The DNA base composition was 45.0 mol% guanine plus cytosine. Numerical taxonomy indicated 70% similarity with known reference Vibrio sp. strains. The 5S rRNA sequence for this strain has been determined: 5'-U G C C U G G C G A C C A U A G C G U U U U G G A C C C A C C U G A U U C C A U G C C G A A C U C A G U A G U G A A A C G A A A C A G C G U C G A U G G U A G U G U G G G G U C U C C C C A U G U G A G A G U A G A A C A U C G C C A G G C A U-3'. Based on the phenetic, molecular genetic, and nucleic acid sequencing data, it is concluded that Vibrio cincinnatiensis represents a new species of the genus Vibrio sensu strictu (as defined by 5S rRNA sequencing results). On a basis of 5S rRNA comparative sequence analysis, the organism appears to share a recent common ancestor with V. gazogenes (98% homology) and close ancestry with V. mimicus, V. fluvialis, and V. metschnikovii.