A number of obligately anaerobic fermentative bacteria are known to degrade a variety of organic substrates such as sugars, amino acids, and others, in the presence of high salt concentrations (up to 3-4 M) to products such as hydrogen, CO> acetate and higher fatty acids, and ethanol. Our understanding of the fate of these products in hypersaline environments is still extremely limited. The occurrence of bacterial sulfate reduction is well established at salt concentrations of up to 24% ; however, the bacteria involved have not yet been isolated in pure culture, and the range of electron donors used is unknown. Halophilic or halotolerant methanogenic bacteria using hydrogen/CO2 or acetate as energy source are notably absent; methanogenesis under hypersaline conditions is probably limited to such substrates as methanol and methylamines, which cannot be expected to be major products of anaerobic degradation of most organic compounds. E x t r e m e e n v i r o n m e n t s are generally inhabited by a limited variety of forms of life, and the m o r e ' e x t r e m e ' the e n v i r o n m e n t , the smaller the n u m b e r of organisms that are able to thrive in it. H y p e r s a l i n e e n v i r o n m e n t s such as the D e a d Sea or the north arm of the G r e a t Salt L a k e , U t a h , are colonized by a limited variety of bacteria and unicellular algae, and only very few higher forms of life, if at all. M o s t studies of life u n d e r high salt concentrations were restricted to the aerobic microflora (the e x t r e m e l y halophilic aerobic bacterial genus Halobacterium, the unicellular green alga Dunaliella, and a few m o r e species), and surprisingly little is k n o w n on anaerobic processes occurring in the sediments of hypersaline water bodies. As late as 1979 it still could be stated that: there have b e e n no published reports on the m i c r o b i o l o g y of anoxic hypersaline e n v i r o n m e n t s ( L a R o c k et al. 1979). A n a e r o b i c d e g r a d a t i o n of complex organic substrates to carbon dioxide and m e t h a n e is never achieved by one m i c r o o r g a n i s m alone, but requires the