Contact hypersensitivity (CHS) requires activation of the innate immune system, and results in an adaptive immune response. Many cells of the innate immune system use Toll-like receptors (TLRs), which signal through the adaptor protein, MyD88, to initiate an immune response. MyD88 is also required for signaling downstream of the IL-1 and Il-18 receptors (IL-1R and IL-18R, respectively). Herein, we studied the MyD88 signaling pathway in the CHS response to DNFB. Mice deficient in MyD88 were unable to mount a CHS response to DNFB. In contrast, mice deficient in Toll/IL-1R-containing adaptor-inducing IFN-Β, TLR2, TLR4, TLR6, and TLR9 had no defect in their ability to respond to DNFB. Although both IL-1R and IL-18R-deficient mice showed a reduced CHS response to DNFB, in bone marrow chimera and adoptive transfer experiments, we found that MyD88 and the IL-18R were required in a radioresistant cell in the sensitization phase of the CHS response. In contrast, similar strategies revealed that the IL-1R was required in a radiosensitive cell in the sensitization phase of the CHS response. Taken together, these data indicate that the IL-1R and IL-18R/MyD88 pathways are required in distinctly different cells during the sensitization phase of CHS.