The aim of this study is to offer a critical opinion of an important chapter in the bibliography of Gregorio Marańon, the key figure of Spanish Medicine in the period between the wars. The biography of the philosopher Amiel, of the emperor romano Tiberio and of the Castilian king Enrique IV are carefully studied. In the research the interpretative criteria offered by Medicine and Psychology have been used. His more important works rebuild the political labor of El Conde-Duque de Olivares, "valido" of Felipe IV, and of Antonio Pérez, registrar of Felipe II. In both works Marañón reconstruct, with exhaustive critical bibliography and documentary support, a historical period covering the last decades of the 16th century and the first half of the 17th. Through his works, Gregorio Marañón proves the efficient value of the use of medical and psychological knowledge in historical research.