A psychrophilic marine bacterium was stable in cold seawater or in a solution containing 0.1 MMg++and 0.5 MNaCl. In water and in a number of monovalent salts, including up to 3.0 MNaCl, turbidity of suspensions fell and some intracellular material was released into the external medium. The cells first became swollen and pale under phase contrast optics and then disintegrated into amorphous aggregates. Divalent salts alone, some in very low concentrations, could maintain cell structure. Effectiveness was in the order Cu++ > Zn++ > Ni++ > Ca++ > Mn++ > Mg++. The polyamine, spermine, was ineffective. In the presence of 0.1 MMg++, NaCl and, less effectively, LiCl and RbCl could maintain structure, but KCl, NH4Cl, CsCl, glucose, and sucrose could not. Sodium phosphate, pH 7.0, caused lysis but other sodium salts maintained structure in the presence of Mg++. For growth, Mg++, NaCl, and traces of other ions were required.Phosphatidases attacking cells at 25 °C and higher required salts for maximum activity. The turbidity of water-lysed cells or of envelopes prepared from mechanically broken cells fell at 25 °C and higher; this fall was also dependent on the presence of salts. If cells were lysed in distilled water, or broken mechanically in the presence of salts, more than half their lipid phosphorus and hexosamine was released from material sedimenting after 30 min at 15 000 × gbut these materials were not degraded into other substances. The released material seemed bound to smaller particles, since most of it sedimented after 1 hour at 100 000 × g. The lipid composition of smaller and larger particles, and of whole cells, was the same.