Under Marie Curies guidance at the Radium Institute, Perey learned how to isolate and purify radioactive elements, focusing on the chemical element actinium (discovered in Curies laboratory in 1899 by chemist André-Louis Debierne). Perey spent a decade sifting out actinium from all the other components of uranium ore, which Curie then used in her study of the decay of the element. Marie Curie died of aplastic anemia only five years after Perey began working with her, but Perey and Debierne continued their research on actinium and Perey was promoted to radiochemist.