The authors evaluated dermal phototoxicity using the world smallest minipig (MMPig: Microminipig). MMPigs were administered 100 mg/kg ciprofloxacin hydrochloride with an infusion pump. The dorsal area of each animal was irradiated with ultraviolet-A irradiation. The left dorsal skin was irradiated at intensities of 5, 10, 15, and 20 J/cm(2), and the right dorsal back skin was set as a nonirradiated site. Gross and histopathological examinations were conducted before irradiation and from 1 to 72 hr after irradiation. Initial changes in the skin were necrosis of the basal and/or prickle cell layer and cellular infiltration from 24 hr after irradiation. Vesicle formation observed from 48 hr after irradiation was considered similar to bullous eruptions, a known side effect of fluoroquinolones in humans. Therefore, the authors suggest that the MMPig may be a useful experimental animal model for dermal phototoxicity studies.