Selenium (Se) is a dietary trace element that is essential for effective immunity and protection from oxidative damage induced by ultraviolet radiation (UVR). Langerhans cells (LC) represent the major antigen-presenting cells resident in the epidermis; a proportion migrate from the skin to the draining lymph nodes in response to UVR. Because it is known that Se deficiency impairs immune function, we determined what effect this has on LC numbers. CH3/HeN mice were weaned at 3 wk and placed on diets containing <0.005 ppm of Se (Se deficient) or 0.1 ppm of Se (Se adequate, control mice). After 5 wk on the diet, the epidermal LC numbers in the Se-adequate group were 966 +/- 51 cells/mm2 and LC counts in the epidermis of the Se-deficient mice were 49% lower (p<0.05). Glutathione peroxidase- I (GPx) activity was measured in the epidermis, lymph nodes, and liver. In the epidermis, the activity of GPx in the Se-deficient mice was only 39% (p<0.01) of that seen in epidermis from Se-adequate mice (1.732 U/mg protein). The mice were then irradiated with one dose of 1440 J/m2 of broadband UVB or mock irradiated. After 24 h, the decrease in LC number after UVB was greater in the Se-adequate mice, (40% decrease) compared to the Se-deficient group (10%). Thus, Se deficiency reduces epidermal LC numbers, an effect that might compromise cutaneous immunity.