It is important to determine how fluorescent antioxidant drugs act as immunomodulators. Since a new T-cell population, namely, extrathymic T cells, has recently been identified in the liver and other immune organs, our attention was focused on how one of the above-mentioned drugs (Lumin-A in this study) affects the distribution of extrathymic T cells and thymus-derived T cells in various immune organs. When Lumin-A was administered into mice daily (10 μg/mouse/day) with intraperitoneal or oral route for 3 wks, its unique effect was observed, depending on the routes. Especially, the oral ad libitum administration of Lumin-A induced a prominent induction of thymus-derived T cells, but not extrathymic T cells, in the peripheral immune organs, the spleen and the liver. The present results suggest that a fluorescent antioxidant drug, Lumin-A, has an ability to induce the thymus-derived T cells, i.e., usual T cells for processing foreign antigens, into the periphery.