The behavior of lambda phage in the Rec(-) strain JC-1569 is compared with that in the Rec(+) strain JC-1557. No difference deemed significant was noted in the adsorption rate, latent period, burst size, frequency of lysogenization, and frequency of vegetative phage recombination. The location of the prophage and its mode of insertion in the Rec(-) lysogen of wild-type lambda (lambda(+)) were inferred to be normal from the results of conjugational crosses. Spontaneous and ultraviolet (UV) irradiation induction of lambda(+) were markedly reduced in the Rec(-) lysogen. On the other hand, thermal induction of a mutant lambda (lambdacI857) lysogen of the Rec(-) strain was not reduced and was only slightly affected by UV irradiation. Phage subject to inhibition by lambda immunity failed to multiply in UV-irradiated cells of the Rec(-) lambda(+) lysogen, whereas those not inhibited by this immunity did multiply. It was concluded that the failure of UV to induce lambda(+) in the Rec(-) lysogen was not due to damage to the prophage, but rather to the inability of the irradiated cells to respond by lifting immunity. Preliminary evidence indicates that a single mutation confers recombination deficiency and the inability to lift immunity after UV irradiation. Possible relationships between recombination and the lifting of immunity are enumerated.