AbstractEscherichia colicells exposed to high temperatures exhibit a progressive loss of viability. We observed two mechanisms of cell death induced by lethal temperatures: with and without lysis. The number of cells lysed by heat decreased at later stages of the growth curve, when cells were pre‐treated at lower temperatures for 10 minutes and when cells were pre‐treated with novobiocin, nalidixic acid and cadmium chloride. Cell lysis was similar in wild type,rpoH,groE anddnaK mutant cells as well as in cells which overproduce heat shock proteins GroE or DnaK. Results using cells aligned for cell division and cells growing at 42°C, 45°C and 47°C suggest that cells near division are more sensitive to lysis and that a high concentration of heat‐shock proteins increases their resistance