Clarification of the spatiotemporal regulation and function of immune cells within the skin is critical to the understanding of the role of immune cells and the skin in immune homeostasis. Here, we describe a novel assay system for monitoring cell movements in the entire body using the photoconvertible fluorescent protein "Kaede"-transgenic (Tg) mice. We can label immune cells by the change in color of Kaede from green to red in these cells following exposure to violet light and track these cells in the entire body. The Kaede-Tg system is an ideal tool for monitoring precise cellular movements between the skin and other anatomical sites in vivo at different stages of the immune response.