Complete sequences of 16S rRNA encoding genes from extreme halophiles Halobacterium saccharovorum, Halobacterium lacusprofundi, and Halobacterium distributum were determined. The polar lipids, particularly the glycolipids, of these and 20 other isolates were also analyzed. Based on both genetic and chemotaxonomic data, the following two novel genera are proposed: Halorubrobacterium (comprising Halorubrobacterium saccharovorum, Halorubrobacterium sodomense, Halorubrobacterium lacusprofundi, Halorubrobacterium distributum, and Halorubrobacterium coriensis) and Natrialba (comprising Natrialba asiatica). Evidence for a third new genus is also presented.