A Gram-negative bacterium designated LA1(T) was isolated from water collected in hypersaline Lake Laysan on Laysan Island in the Northwestern Hawaiian Islands. Cells occurred singly as fine rods to short filaments. Growth in 50 % strength marine broth occurred optimally when the medium contained 7.5-10 % (w/v) NaCl. The major fatty acids in LA1(T) grown at 15 and 30 degrees C were 12-methyl tetradecanoic acid and 13-methyl tetradecanoic acid, respectively. The nucleotide sequence of the 16S rRNA gene showed that LA1(T) belonged in the Cytophaga-Flavobacterium-Bacteroides (CFB) group in the domain Bacteria. The closest described neighbour in terms of 16S rRNA gene sequence identity was Psychroflexus torquis ACAM 623(T) (94.4 % over 1423 bases), an obligate psychrophile from Antarctic sea-ice. The G+C content of 35.0 mol% was consistent with this affiliation. Phenotypic and genotypic analyses, including DNA hybridization, indicated that LA1(T) could be assigned to the genus Psychroflexus but, based on significant differences, including growth at 43 degrees C, it constitutes a novel species, Psychroflexus tropicus sp. nov., for which LA1(T) (=ATCC BAA-734(T)=DSM 15496(T)) is the type strain.