We describe the first case of drug-induced solar urticaria due to repirinast, an antiallergic drug developed and introduced into the market in Japan in 1987. The patient was a 72-year-old woman who had been on repirinast for 1 year and 8 months. She developed urticaria immediately after an irradiation with 1.5 J/ cm of UVA, and the provocation test confirmed that repirinast was responsible for the urticarial reaction. The action spectrum of the urticarial reaction was deduced to be 320–350 nm. Passive and reverse passive transfer test results were both negative. However, intradermal injection of patient serum, obtained while she was on repirinast and irradiated in vitro with UVA, demonstrated positive reactions both in the patient and in a normal volunteer. Our findings suggest that nonallergic mechanisms are involved in the reaction. However, the rarity of the phenomenon also suggests an association with some allergic mechanism