The influence of water activity (aw ) on growth, respiration, and Na and K content of cells during respiration has been studied for Salmonella oranienburg. Sucrose, glucose, glycerol, NaCI, and KCI were added to control aw' The organism grew in a glucose-inorganic salts medium at 0�97 a", when any of these solutes was used to adjust a,v, but at 0�96 aw only when glycerol was employed. Respiration was not inhibited in glycerol-adjusted solutions at am's at which the rate was very low in other solutes. When a", was controlled by sucrose or glucose, cells oxidizing glucose accumulated K but not Na. Accumulation of K was greatest at 0�975 aw In solutions of NaCI, accumulation of K was small and in glycerol solutions it was absent. The differences between glycerol and the other solutes tested are discussed.