Infection of Escherichia coli by phage [lambda]22 in 0.02[image]-Sr(NO3)2, CaCl2 or MnSO4 occurred as readily as in 0.02[image]-MgSO4. The response of bacteria infected in the presence of Sr2+, Ca2+ and Mg2+ was predominantly lysogenic, but infection in 0.02[image]-Mg2+ gave a higher lysogenic response (90%) than with the other cations tested. With Mn2+ in optimal conditions at least 25% of the infected bacteria always gave the lytic response. When the newly infected bacteria were transferred to a growth medium, a period of about 40 min. had to elapse before the prophage could be detected by zygotic induction by mating with a non-lysogenic F- organism. A period of about 100 min. was required before all the bacteria giving the lysogenic response could be induced by ultraviolet radiation.