The protective effect of sodium-L-ascorbyl-2 phosphate (As-2P), a stable form of ascorbic acid (AsA), against photodamage induced by a single dose of UVB exposure (290-320 nm, Max 312 nm) was investigated using cultured mouse skin. When the cultured skin was treated with various As-2P concentrations, the cutaneous AsA level increased in proportion to the As-2P concentration. After 3 h of incubation, the AsA level in the cultured skin treated with 2, 20 and 100 mM As-2P increased 1.03-, 2.17- and 6.27-fold, respectively, compared with that of the control skin. These results suggest that As-2P was transported into the cultured mouse skin where it was converted to AsA. After 3 h, the cutaneous AsA level in irradiated (20 kJ/m2) skin was depleted to a half of that in the control skin. However, the level in skin pretreated with 20 mM As-2P was maintained within normal limits, even after 24 h. Pretreatment with 20 mM As-2P significantly prevented such photodamage as sunburn cell formation, DNA fragmentation and lipid peroxidation, which were caused by a single dose of UVB irradiation. These results suggest that the protective effect of 20 mM As-2P on UVB-induced cutaneous damage is due to the maintenance of a normal As level by conversion of As-2P to As in skin tissue.