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The effects of temperatures of 50 and 60 C on log-phase and stationary-phase cell suspensions of Staphylococcus aureus are described. There is a leakage of free amino acids, protein, and 260 mμ-absorbing material from both types of cell suspension, and membrane damage, as measured by the intracellular penetration of 8-anilino-1-naphthalene-sulfonic acid, may be partially related to this leakage. Ribonucleic acid (RNA) degradation at any one temperature is virtually the same for both types of cell suspension, proceeding initially at a more rapid rate at 60 C than at 50 C. However, at the lower temperature, there is a secondary breakdown of RNA, which may be the result of enzyme action on a particularly labile RNA fraction. With stationary-phase cell suspensions heated in 1 m sucrose, there is a more rapid degradation of RNA at 60 C than with cells in water. The results are discussed in relation to the biochemical effects of moist heat on the organism.