Following skin sensitization of mice, epidermal Langerhans cells (LC) are stimulated to migrate via the afferent lymphatics to the draining lymph nodes. Previous studies have demonstrated that, while in transit, LC acquire the characteristics of mature dendritic cells (DC) and develop into potent immunostimulatory cells. In the present study the expression by LC and lymph node DC of intercellular adhesion molecule-1 (ICAM-1) has been compared. Freshly-isolated LC expressed only very low levels of ICAM-1. In contrast lymph node DC, irrespective of whether they were isolated from resting lymph nodes or from activated lymph nodes draining the site of sensitization with oxazolone, exhibited significant membrane ICAM-1. As a substantial proportion of the DC found within the draining nodes of skin sensitized mice derive from epidermal LC it is apparent that, during migration from the skin, LC are induced to express increased ICAM-1. Such is compatible with the development of LC into effective antigen presenting cells.