Labelled non-viscous cells ofMicrococcus halodenitrificanswere obtained in media containing P32and 2 Msodium chloride and their growth then followed in salt concentrations ranging from 0.55 M, the lower limit of growth, to 3 M. At concentrations of 0.7 Mand above, cells remained non-viscous and only traces of extracellular nucleic acids (NA) could be detected. At lower concentrations of salt, cells became viscous and the amount of extracellular NA increased as the concentration decreased. The distribution of P32indicated that the source of the extracellular NA was intracellular. At the salt concentrations studied, the loss of NA was prevented by the addition of calcium or magnesium ions. However, sodium chloride seemed necessary to maintain the cell wall ofM.halodenitrificansand the effect was supplemented by divalent ions. It is suggested that this may explain the salt requirement of this organism and possibly that of other halophilic bacteria.