Systemic contact dermatitis may occur in contact-sensitized individuals when they are exposed to haptens orally, transcutaneously, intravenously or by inhalation. We report the case of a woman developing a diffuse skin eruption after the topical use of Rhus toxicodendron alcoholic extract and the oral introduction of a homeopathic preparation of the same substance for herpes treatment. An open test, performed with the Rhus toxicodendron tincture, showed an erythemato-oedematous response at 48 h and vesicular reaction at 96 h that was still present after 7 days. Patch test with 65% ethyl alcohol gave negative results. The open test performed, as control, in eight healthy informed subjects revealed negative responses to Rhus tincture application. The result is interesting because in Italy, allergic contact dermatitis to Rhus is uncommon and this case increases the understanding of the pathogenetic mechanism leading to systemic contact dermatitis development.