Following contact sensitization of mice there is a rapid accumulation of dendritic cells (DC) within lymph nodes draining the site of exposure. Previous studies have revealed that cells bearing high levels of contact allergen can also be identified within the low buoyant density fraction of draining lymph node cells, and it has been assumed that the majority of these are DC. The purpose of the present study was to establish the phenotypic characteristics of the antigen-bearing cells which appear in lymph nodes within hours of skin painting with contact allergens, including the contact sensitizing fluorochromes fluorescein isothiocyanate (FITC) and rhodamine B isothiocyanate (RITC). Indirect immunofluorescence and two-colour immunofluorescence analyses revealed that initially all antigen-bearing cells which arrive in the draining lymph nodes express class II MHC antigens and exhibit a dendritic morphology. Phagocytic cells, cells reactive with F4/80 and anti-Mac-1 antibodies and lymphoblasts are not associated with detectable levels of antigen. In addition, although Thy-1+ cells co-fractionate with lymph node DC they are not dendritic in nature and are not associated with antigen. These data are compatible with the hypothesis that following skin sensitization epidermal Langerhans' cells bind antigen and transport it to the regional lymph nodes. In addition, it is clear that the recently described population of Thy-1+, Ia- dendritic cells within the murine epidermis do not perform a similar function.