We examined sensitization and crossreaction by the guinea pig maximization test (GPMT) with phenolic compounds. Skin specimens were collected from earlobes of BALB/c mice on 24 h after elicitation phase of contact hypersensitivity reaction (CHR) with phenolic compounds. The expression of cytokines of skin specimens was examined by the reverse transcriptase/polymerase chain reaction (RT-PCR) method. Consequently, phenolic compounds which showed positive reaction in GPMT expressed IL-2 and IFN-gamma on 24 h after elicitation, and some phenolic compounds showed marked crossreaction. Therefore, it was found that on several phenolic compounds, dimerization of these compounds from monomer to dimer decrease sensitization.