The taxonomic position of eight fluorescent Pseudomonas isolates, from two Lebanese spring waters, which were previously recognized by numerical analysis as members of a new subcluster (subcluster Vb) was examined. Except for one strain, the new subcluster exhibited internal DNA hybridization values of 76-100%, and 9-53% hybridization was measured with the type or reference strains of other Pseudomonas species. The highest DNA binding value was found with Pseudomonas marginalis strains (37-53%). The G+C content of the DNA of the type strain was 58 mol%. A comparison of 1322 nt of the 16S rRNA gene sequence of the strain representing subcluster Vb (CFML 96-195T) with the sequence of other strains of the genus Pseudomonas revealed that strain CFML 96-195T was part of the 'Pseudomonas fluorescens intrageneric cluster'. On the basis of the results of phenotypic, DNA-DNA and phylogenetic analyses, a new Pseudomonas species, Pseudomonas libanensis sp. nov., is proposed for the seven strains of subcluster Vb. The type strain is P. libanensis CFML 96-195T and has been deposited in the Collection de l'Institut Pasteur (Paris, France) as CIP 105460T. The P. libanensis strains are phenotypically and genotypically homogeneous and can be differentiated from most other fluorescent species by several phenotypic features. Differentiation of P. libanensis and Pseudomonas aeruginosa is based mainly on pyocyanin production; P. libanensis can be differentiated from P. fluorescens (all biovars) by alpha-aminobutyrate assimilation. The clinical significance of P. libanensis is unknown.