We have revealed that local stimulation of sensory neurons is involved in the adjuvant effect of dibutyl phthalate (DBP) in a fluorescein isothiocyanate-induced mouse contact hypersensitivity model. Transient receptor potential (TRP) A1 and TRPV1 seemed to be candidate DBP targets. Here we directly demonstrated that DBP activates a subset of neurons in mouse dorsal root ganglia responsive to TRPA1 and TRPV1 agonists. TRPA1 and TRPV1 activation was further demonstrated using cultured cells expressing TRP channels. Among structurally different phthalate esters, there is a positive relationship between the activation of TRPA1- or TRPV1-expressing cells and the adjuvant effect. (C) 2008 Elsevier B.V. All rights reserved.