Prostaglandin E1 (PGE1) ointment has been shown to improve the survival of skin grafts. However, the mechanism of the effects of PGE1 through topical application is unknown. A rat skin flap model was used to determine whether PGE1 is absorbed through the intact skin. The prostaglandin concentrations in the flaps in the study group were greater than those in the controls. It is suggested that PGE1 is absorbed through the skin.