Rafael Lorente de Nó was the last disciple of Santiago Ramón y Cajal. He initiated, together with Fernando de Castro, the physiological orientation of Cajal's histological school. His development as a researcher reveals the difficulties that Cajal's disciples had to face in order to progress from neurohistological to neurophysiological research. The correspondence between Ramón y Cajal and Lorente de Nó during this period (1930-1934), published here, clearly shows these problems. We also attempt to diminish the important gap in Spanish historical-medical research presented by the letters of Ramón y Cajal.