The induction of edema and pyrimidine dimers in epidermal DNA was determined in the skin of SKH:HR1 mice exposed to graded doses of ultraviolet radiation AI (UVAI; 340–400 nm). Exposure to UVAI induced 1.6 ± 0.08 × 10⁻⁶ (mean ± standard error of mean) pyrimidine dimers per 10⁸ Da of DNA per J/m². Edema in irradiated animals was determined as an increase in skinfold thickness. A dose of 1.8 × 10⁶ J/m² of UVAI that resulted in a 50% increase in skinfold thickness (SFT_50%) would have induced 1.0 × 10⁵ dimers per basal cell genome. A similar increase in SFT induced by full spectrum solar ultraviolet radiation (290–400 nm) would accompany the induction of 11.0 × 10⁵ pyrimidine dimers per basal cell genome. These results support a hypothesis that UVAI-induced pathological changes of the skin are mediated through the formation of nondimer photoproducts.