The halobacterium Haloferax mediterranei accumulates poly(beta-hydroxybutyrate) (PHB) as intracellular granules. The conditions for PHB production in batch and continuous cultures have been studied and optimized. Phosphate limitation is essential for PHB accumulation in large quantities. Glucose and starch are the best carbon sources. With 2% starch, 0.00375% KH(2)PO(4), and 0.2% NH(4)Cl in batch culture, a production of ca. 6 g of PHB per liter was reached, being 60% of the total biomass dry weight, and giving a yield over the carbon source of 0.33 g/g. The PHB production in continuous cultures was stable over a 3-month period. Our results demonstrate that H. mediterranei is an interesting candidate for industrial production of biological polyesters.