Background: Long-term sun exposure can cause major alterations in the papillary dermis, resulting in the deposition of massive amounts of abnormal elastic material, termed solar elastosis. Previous work has demonstrated that this type of photodamage is accompanied by an increase in elastin and fibrillin messenger RNAs and elastin promoter activity. Objective: Our purpose was to develop a rapid and sensitive in vivo method for evaluating compounds offering protection against cutaneous photodamage. Methods: Using a line of transgenic mice that expresses the human elastin promoter linked to a chloramphenicol acetyltransferase reporter gene, we applied sunscreens with various sun protection factors to 5-day-old mice followed by 30 minimal erythema doses of solar simulating radiation for three consecutive days. Results: Solar simulating radiation alone resulted in a fivefold increase in elastin promoter activity. Sun protection factors of 2, 4, 8, and 15 yielded a reduction in promoter activity by 2.8%, 42.5%, 58.1%, and 70.3%, respectively. Conclusion: These results confirm the use of this system as a rapid and sensitive in vivo model for evaluating compounds that protect against photodamage. (J Am Acad Dermatol 1997;37:725-9.)