Following topical exposure of mice to skin-sensitizing chemicals, Langerhans cells (LC), many of which bear antigen, are stimulated to migrate via the afferent lymphatics to draining lymph nodes. Consistent with the acquisition of potent immunostimulatory activity, LC while in transit to lymph nodes, are subject to a functional and phenotypic maturation thought to be mediated by granulocyte/macrophage colonystimulating factor (GM-CSF) and possibly other epidermal cytokines. An interesting question is the nature of the stimulus that initiates the migration of LC from the epidermis. We have examined the influence of intradermal tumor necrosis factor α (TNF-α), another epidermal cytokine, on the accumulation of dendritic cells (DC) in draining lymph nodes. Murine, but not human, recombinant TNF-α caused a rapid and concentration-dependent increase in the frequency of DC in draining nodes. The conclusion drawn is that local production of TNF-α provides one signal for LC migration during cutaneous immune and inflammatory responses.