Topical dinitrochlorobenzene (DNCB) is often used for evaluating contact skin hypersensitivity in immunocompromised patients. We have determined, in this study, that topical application of DNCB alone, even without induction of contact skin hypersensitivity, was sufficient to observe activation of the human immunodeficiency virus promoter (long terminal repeat) in the skin of an HIV-1 long terminal repeat-luciferase transgenic mouse model. Such treatment might be contraindicative in patients infected with the human immunodeficiency virus, because in earlier studies DNCB-exposed skin dendritic cells might migrate into draining lymph nodes which play an important role in AIDS pathogenesis.