Non-growing cells of a psychrophilic marine bacterium lyse if subjected to temperatures above 21 °C, to low ionic strengths, or to pH values below 6.0. Microelectrophoretic techniques were used to help determine the surface effects of cellular breakdown. During lysis, however induced, the cell populations became heterogeneous in mobility. This was apparently due to the adsorption of intracellular material, with a higher negative charge than intact cells, onto the cell surface. The mobilities of cells lysed in water or at acid pH reverted to the control values after repeated washings, which were thought to remove adsorbed intracellular material. Lysis induced by these latter treatments, therefore, did not involve the external cell surface. Water-lysed cells were stable at temperatures where both whole cells and mechanically prepared cell envelopes were subject to breakdown. After temperature-induced lysis, the washed cells possessed a higher negative mobility than intact cells, which was not due to the presence of adsorbed intracellular material, but rather to an irreversible surface change. Lysis in distilled water at 25 °C left the cell surface unchanged, and the "temperature effect" of a permanently increased negative charge was only evident when lysis at 25 °C preceded exposure to distilled water.