Some species of extremely halophilic archaebacteria, Halobacteriaceae, have been shown to accumulate large amounts of poly (beta-hydroxybutyrate) under conditions of nitrogen limitation and abundant carbon source. The production of poly (beta-hydroxybutyrate), at least in large quantities, was restricted to two carbohydrate-utilizing species, Halobacterium mediterranei and H. volcanii. In addition to the nutrients in the media, the salt concentration also influenced poly (beta-hydroxybutyrate) accumulation, which was greater at lower salt concentrations. The possible application of these microorganisms for the production of biodegradable plastics is discussed.