Heterophyllaea pustulata (Rubiaceae), a South American genus, is a phototoxic shrub that grows in the Andean mountain range of the northwest of Argentina, popularly known as "cegadera". Animals that ingest the aerial parts of this plant suffer a typical primary photosensitization reaction, clinically revealed by dermatitis and blindness in severe cases. Anthraquinone derivatives (AQs), the main metabolites of this species, are characterized as Type I and/or Type II photosensitizers according to their physicochemical properties. The natural toxicity conditions were reproduced in vivo assays by oral administration of soranjidiol and rubiadin, the main components of the aerial parts. By HPLC analysis, the presence of these AQs was determined in serum and quantified in the skin of experimental animals.