We previously demonstrated that combined treatment of mice with crude oil and longwave ultraviolet radiation (UVA) led to the depletion of IA‐positive cells from the epidermis. In the present study, we have developed an in vitro screening assay for combined effects of purified petrochemicals and UVA on epidermal IA and Thy‐1 expression. This method involves removal of skin from donor mice prior to treatment with chemicals and UVA (20,000 J/m2), followed by in vitro culture and subsequent immunoperoxidase staining. In this study, a complete correlation was observed in terms of IA‐positive cell density among similarly treated cultured skin and live mice. In vivo and in vitro studies both indicated that anthracene but not phenanthrene or benzo[a]pyrene led to significant depletion of both epidermal Langerhans cells and Thy‐1‐positive dendritic cells when followed by UVA treatment. The in vitro assay developed for this study should prove to be a valuable tool for the screening of a wide variety of chemicals for contact photosensitizing activity.