Several chloroformic extracts containing some sesquiterpene lactones from autochtonous plants ofParthenium hysterophorus, collected in the province of Salta (Argentina), were separated and identified by high performance reversed-phase liquid chromatography with C18column and propanol-water mobile phases, using gradient elution and concentrations of propanol larger than 10% (v/v). Lactones previously purified and characterized by H1RMN, C13RMN, IR, and mass spectrometry, were used as standards.