When suspensions of Staphylococcus aureus were stored at different temperatures in water or m sucrose, an increase or decrease (depending on the temperature of storage and the nature of the environment) in o.d. and light scattering properties occurred. Such changes were related to changes in cell size, leakage of intracellular constituents from the cells and precipitation of cytoplasmic material. Electron micrographs of ultrathin sections of cells illustrated some of these changes. The results demonstrated that caution was necessary in the interpretation of changes in o.d. and light scattering properties of this organism. Copyright © 1969, Wiley Blackwell. All rights reserved