The effects of an exposure to 6 times the minimal erythemal dose of ultraviolet radiation (UV) were studied using a visual scale and a tri-stimulus colorimeter in 12 sun-tolerant (skin types III and IV) patients with type A dysplastic nevus syndrome. In such individuals, the melanocytic system would be susceptible to neoplastic transformation induced by sunlight. The cutaneous response to a marked UVB erythema has been shown to identify the high-risk patients prone to light-induced skin cancer. This study indicates that the UVB cutaneous susceptibility of patients with type A dysplastic nevi is not significantly different from control subjects, in terms of erythemal and tanning response.