Since its definition in 1975, the MN scale for the Neogene has been the subject of increasing criticism. This biochronologic classification has been widely used by many geologists and large mammal specialists. In this paper, we propose to redefine the meaning and content of the MN "zones", which, in this paper, are considered as biochronologic units and not true biozones. This redefinition is made in three steps: 1. Definition of a true succession of biozones with stratigraphic support. This general biozonation is a consequence of the congruence observed among the local biozonations proposed for several basins in Spain: Ebro, Calatayud-Daroca, Valles-Penedes, Duero, Teruel, Madrid and Guadix-Baza. 2. Correlation of the main mammal bioevents associated to each biozone in these sections. 3. Proposal of long distance correlations based on the succession of some selected mammalian events. According to this scheme, 24 biozones have been recognized for the Spanish Neogene and the 17 MN units are referred to.