The pasteurization effect of far-infrared (FIR) radiation on Escherichia coli suspended in physiological phosphate buffered saline in the exponential growth phase (exponential phase) was studied, FIR irradiation decreased the number of viable cells in their exponential phase more rapidly than that in their stationary growth phase (stationary phase). By using four kinds of antibiotics as selective reagents to examine the injuries of bacteria, the damaged parts induced by FIR irradiation were specified on the basis of the changes in sensitivities to selective reagents, FIR irradiation damaged mainly RNA ploymerase off, coli in the exponential phase. Under the condition that the transient behavior of the bulk temperature of bacterial suspension irradiated by FIR was the same as that heated by thermal conduction, the pasteurization effect by FIR irradiation on the exponential phase cells was much greater than that by thermal conduction. However, both FIR irradiation and thermal conductive heating induced similar changes in the sensitivities to selective reagents for the exponential phase cells off. coli. Under the same irradiation conditions, the changes in sensitivities to the selective reagents for the exponential phase cells were different from those for the stationary phase cells. The injuries of ribosome in the exponential phase cells were not as serious as those in the stationary phase cells. It was suggested that the mechanisms of death of the exponential phase cells and the stationary phase cells were different from each other.