Skin fibroblast cells obtained from an individual displaying the disease nevoid basal cell carcinoma syndrome (NBCCS) were exposed to the stimulated sunlight produced by a solar simulator. It was found that the NBCCS cells were significantly more sensitive to simulated sunlight-irradiation compared with skin fibroblasts obtained from a normal human subject. In addition, the NBCCS cells were slightly more sensitive to x-irradiation. In contrast, the two cell strains exhibited comparable sensitivity to 254 nm UV. The repair of the principal DNA damages induced by treatment with simulated sunlight was examined in the NBCCS and normal cells. For all of the photoproducts examined, the response of the two cell strains was nearly identical. Hence, although the NBCCS cells exhibited a hypersensitivity to simulated sunlight, these cells appear to be proficient in the repair of the DNA damages induced by simulated sunlight exposure.