Doses of ultraviolet (UV) irradiation up to 40 Jm-2 produce a continuous increase of both the level and the rate of ATP production in a RecA+ strain of Escherichia coli growing in AB minimal medium with glucose as carbon source. At fluences higher than 40 Jm-2, these two parameters increase at a constant rate independent of the dose. Furthermore, in the UV-irradiated recA13 mutant, the concentration of ATP is higher and its rate of production is faster than in the RecA+ strain. The same behavior as cited above was shown by both RecA+ and RecA- cells when incubated in AB minimal medium without any carbon source both 60 min before and after UV irradiation. © 1986 Springer-Verlag New York Inc.