Pasteurella pestis, harvested after 24 to 30 hours of growth in a casein hydrolyzate medium at 26 deg C, was resuspended and shaken in 3% lactose - 0. 1 M phosphate buffer for 4 hours at the same temperature. Certain characteristics of these starved cells were compared with those of control cells. No differences in the amounts of cellular carbohydrate or lipid were detected. The concentrations of the principal free amino acids were greater in the shaken cells, except that they contained no measurable arginine, and the normally large pools of intracellular tricarboxylic acid cycle intermediates were reduced. Greater viable cell counts resulted with the cells that were shaken in lactose buffer than with the control cells when each was incubated at 5 deg C for several weeks. However, the reduced viabilities were apparent losses caused by the formation of aggregates of cells. The clumping of cells was caused by the polymerization of extracellular nucleic acids, principally deoxyribonucleic acid, that were excreted by the cells. Cell clumping could be partially prevented by prior shaking of the suspended cells which removed some of the deleterious material, or by the action of crystalline deoxyribonuclease.