Friedrich Nietzsche’s criticism towards the substance-concept „I“ plays an important role in his late thought, and can be properly understood by making reference to the 19th century debate on the scientific psychology. Friedrich Lange and Ernst Mach gave an important contribution to that debate. Both of them developed the ideas of Gustav Fechner, and thought about a „psychology without soul“, i.e. an investigation that gives up with the old metaphysics of substance in dealing with the mind-body problem. In this paper I shall deal with both Lange and Mach (whose writings has been read by Nietzsche), in order to shed some light on Nietzsche’s rejection of the „I“ in philosophy.