Summary 7,12-Dimethylbenz[ a ]anthracene (DMBA)-treated hairless mice exposed to UVB radiation were used to examine the effect of graded levels of vitamin B 6 [1, 7 or 35 mg pyridoxine (PN) HCl/kg] on skin tumorigenesis for 18 wk. Compared to the 1 mg PN HCl/kg diet, the 35 mg PN HCl/kg diet significantly elevated the incidence and multiplicity of skin tumors, while there was no difference in skin tumorigenesis between the 7 and 35 mg PN HCl/kg diets. Skin levels of oxidative stress markers (lipid peroxides and protein carbonyls) were unaffected by dietary treatment. Compared to the 1 mg PN HCl/kg diet, the 7 and 35 mg PN HCl/kg diets significantly elevated serum pyridoxal 5 ¢ -phosphate (PLP) without affecting the skin level of PLP. The results suggest that dietary supplemental vitamin B 6 exaggerates UVB-induced skin tumorigenesis in hairless mice without affecting oxidative stress in the skin.