The effect of water activity (a(w)) on the heat resistance of eight strains of Salmonella was studied. Heat resistance of the organisms increased as the a(w) of the heating menstruum was reduced. Sucrose afforded the cells a greater degree of protection than did fructose, glycerol, and sorbitol. A direct correlation between a(w) and heat resistance could not be established over the range of a(w) levels tested in this study. There was variation among the strains of salmonellae in the magnitude of the increase in heat resistance as the a(w) level was reduced. All strains of Salmonella tested showed a greater increase in heat resistance than S. senftenberg 775W as the environment became drier. Washed cells had D values 25 to 75% lower than unwashed cells. Prior growth of the organisms in media with a reduced a(w) increased the heat resistance of the organisms when glycerol, but not when sucrose, was the controlling substance.