In 1888, the spiritist Ercole Chiaia challenged Cesare Lombroso to go to Naples and study a brilliant though still unknown medium: Eusapia Palladino. At that time Lombroso turned down the challenge. However, in 1891 he became fascinated by the medium's phenomena. Despite the abundant literature on Palladino, there is still an episode that needs to be explored: in 1888, the Spanish doctor Manuel Otero Acevedo accepted the challenge rejected by Lombroso, spent three months in Naples studying the medium and invited the Italian psychiatrist to join his investigations. This unexplored episode serves to examine the role of scientific authority, testimony, and material evidence in the legitimization of mediumistic phenomena. The use Otero Acevedo made of the evidence he obtained in Naples reveals his desire to proclaim himself an authority on psychical research before other experts, such as Lombroso, Richet, and Aksakof.