Escherichia coli has been reported previously to produce copious indole as a response to high temperature (50℃) and this indole is thought to aid survival. We reinvestigated this phenomenon and found that E. coli may produce indole when growth is absent which is a consequence to elevated temperature, but not as a direct response to heat stress. Moreover, indole thus produced (300μM) has no effect on viability. Interestingly, indole at a very low concentration, 20 μM, can rescue a indole-negative strain (ΔtnaA) under heat stress conditions.