In accordance with Recommendation 30b of the International Code of Nomenclature of Bacteria, which calls for the development of minimal standards for describing new species, we propose minimal standards for descrip- tion of new taxa in the order Halobacteriales. The minimal standards include information on the following characteristics: cell morphology; motility; pigmentation; the requirement for salt to prevent cell lysis; optimum NaCl and MgCl2 concentrations for growth and range of salt concentrations enabling growth; temperature and pH ranges for growth; anaerobic growth in the presence of nitrate or arginine; acid production from a range of carbohydrates ; ability to grow on single carbon sources; catalase and oxidase tests; hydrolysis of starch, casein, and Tween 80; sensitivity to different antibiotics; and polar lipids. The placement of a new taxon should be consistent with phylogeny, which is usually based on 16S rRNA nucleotide sequence information, and with DNA-DNA hybridization data in the case of descriptions of new species. This proposal has been endorsed by the members of the Subcommittee on the Taxonomy of Halobacteriaceae of the International Committee on Systematic Bacteriology. In accordance with Recommendation 30b of the Interna- tional Code of Nomenclature of Bacteria (21), which calls for the development of minimal standards for describing new species, we propose minimal standards for descriptions of new taxa of aerobic halophilic archaea (order Halobacteriales). General principles. The purpose of this article is to provide microbiologists involved in the taxonomy of the aerobic halo- philic archaea (order Halobacteriales, family Halobacteriaceae; also called halobacteria below) a framework for studying them. Adherence to the suggested minimum standards below should help stabilize the taxonomy of the Halobacteriales. With the consent and support of the Subcommittee on the Taxonomy of Halobacteriaceae we have adopted a polyphasic view of halophile taxonomy as suggested by Murray et al. (26). We recommend that all future taxonomic publications on the Halobacteriales should contain data on phenetic, chemical, and molecular properties. We thus recognize that modern natural classification requires as complete a data set as possible, in- cluding phenotypic and genotypic information. Table 1 provides a list of the presently recognized genera and species in the Halobacteriales. The current classification is based on the following three kinds of data: (i) phenotypic data, such as cell morphology, growth properties, etc. (34); (ii) chemical data, especially the patterns of polar lipids present in the membranes (34, 36) (differences in polar lipid patterns have been particularly important at the genus level); and (iii) 16S rRNA sequence information and DNA-DNA hybridiza- tion data. During the last few years a fairly complete database of 16S rRNA sequences of the type strains of the species in the Halobacteriales has become available and has enabled the con-