A simple chemically defined minimal medium consisting of sodium glutamate, glucose, vitamins, and salts was devised to support growth of the moderate halophile, Vibrio costicola, over as wide a range of NaCl concentrations as the complex medium, proteose peptone + tryptone. The lag period at higher NaCl concentrations was longer in the chemically defined minimal medium than in proteose peptone + tryptone. Chemically defined minimal medium also supported the growth of an unidentified moderate halophile, HX, and of Vibrio alginolyticus and Vibrio cholerae. The Mg2+ concentration required for good growth changed with the growth temperature for both V. costicola and HX.