Twenty-four hours after skin painting mice on the flank with the contact sensitizer fluorescein isothiocyanate (FITC), the number of dendritic cells (DC) increased sharply, not only in draining but also in contralateral (CLN) and distant lymph nodes. High levels of antigen were detected on up to 50% of DC isolated from draining lymph nodes (DLN), and these cells were potent stimulators of naive T cells in vitro. Less than 3% of DC from contralateral and distant lymph nodes carried detectable antigen and did not induce significant T-cell proliferation. A significant number of DC had migrated to draining, contralateral and distant lymph nodes without acquiring detectable antigen. This indicates that there is a systemic signal causing the movement of DC to lymph nodes. This appears to be independent of mature T cells, as the systemic migration of DC also occurred in nude mice.