As a teenager, de los Reyes had been intrigued by the growing interest in the "new science" of "El saber popular" (folklore). On March 25, 1884, Jose Felipe Del Pan wrote an article in "La Oceania Filipina" calling readers to contribute folklore articles, inspired by interest in the subject in the peninsula. De los Reyes was urged by del Pan to contribute and gave him books on the subject pique his interest. Two months later, de los Reyes submitted his articles concerning the folklore of Ilocos, Malabon, and Zambales. In 1887, at the age of 23, del Pan compiled de los Reyes' articles and submitted them to the "Exposición General de las Islas Filipinas" in Madrid, where he won a silver medal. These articles would eventually become one of his most important contributions to Philippine studies, "El Folk-lore Filipino". "Folk-Lore" was published in 1889 in two volumes.