Introduction: To study the effect of ultraviolet B (UVB) radiation on human epidermal Langerhans cells (LC), normal human skin was irradiated ex vivo with single doses of UVB.Materials and Methods: LC that spontaneously migrated from epidermal sheets during overnight culture were used to assess possible effects of UVB on the T-cell stimulatory function. Full-thickness skin biopsies were used to study alterations in migratory properties.Results: UVB exposure of epidermal sheets caused a reduction of the percentage of HLA-DR positive cells migrating from the sheets, as well as an impaired capacity to induce proliferation of allogeneic T cells, when compared to cells migrating from nonexposed control sheets. When a correction was made for the decreased number of HLA-DR positive LC migrating from the irradiated epidermis, however, it appeared that on a per cell basis the T-cell stimulatory capacity was identified for LC migrating from UVB-exposed and nonexposed epidermis. UVB-induced thymine-dimers could be demonstrated in the LC from UVB-treated skin. The presence of this DNA damage indicates that the LC had received significant doses of UVB. As concerned the migratory properties of LC, we found that UVB radiation reduced the numbers of CD1a positive LC migrating from the irradiated full-thickness skin, but also that UVB exposure reduced the numbers of CD1a positive LC in the epidermis. This indicates that UVB causes death of LC or possibly loss of cell surface molecules rather than altering LC migration.Conclusion: LC that are still able to migrate from UVB-exposed skin fully retain their capacity to activate allogeneic T cells, despite the presence of DNA damage.