The elastosis-inducing capacity of UV-A and UV-B was studied in the skin of hairless mice. After irradiation with UV-B and UV-A applied either simultaneously, separately or sequentially, the degree of elastosis in the dermis was microscopically evaluated. This semi-quantitative method showed no significant elastosis in the UV-A irradiated mice, and moderate elastosis in the UV-B irradiated mice. Heavy elastosis was observed when the mice were exposed sequentially to UV-B and a large dose of UV-A, but if a moderate dose of UV-A was given simultaneously with UV-B, the degree of elastosis was slightly reduced compared with the elastosis induced by UV-B alone.