Spleen cells from newborn mice are immunologically nonreactive and do not respond by proliferation upon stimulation with the T cell mitogen concanavalin-A (Con-A) or with recombinant interleukin-2 (IL-2). We have found that, in spite of the observed non-reactivity in the proliferative tests, cells from newborn mice were able to synthesize a significant level of mRNA for gamma-interferon (gamma-IFN) after stimulation with IL-2, but did not synthesize gamma-IFN upon stimulation with Con-A. Since gamma-IFN is of prime importance for antiviral and fungicidal activities and has complex regulatory functions for the cells of the immune system, we suggest that it could play an important role in the survival of newborns.