Natural killer (NK) cell-mediated contact sensitivity was recently described in mice. Here, we confirm NK cell-mediated contact sensitivity (CS) in SCID and RAG1−/− mice but not in SCIDbeige mice, which have non-functional NK cells that lack NK cell granules. NK cell-mediated CS was transferred by liver mononuclear cells and the DX5+ fraction of liver cells, confirming that NK cells mediate CS in the absence of T and B cells. Participation of NKT cells and B-1 cells was ruled out using Jα18−/− and JH−/− mice, respectively. Remarkably, NK cell-mediated CS was observed just 1 hr after immunization and was detectable as early as 30 min after challenge. Further, we examined cytokine requirements for NK cell-mediated CS, and found that liver mononuclear cells from interleukin-12−/−, interferon-γ−/− and interferon-α receptor−/− donors fail to transfer NK cell-mediated CS to naive hosts. Our studies clearly show that dinitrofluorobenzene sensitized NK cells mediate very rapid, antigen-specific cell-mediated immunity, with features of both innate and acquired immune responses.