The failure of cut axons to grow along fibre tracts in the adult CNS contrasts with their ability to do so in development. Organotypic slices culture of a number of areas enables the time of failure to be pinpointed to around the second week of postnatal life in the rat. ‘Heterochronic’ co-culture of slices above and below this age shows that the failure is due to the inability of the older axons to grow into either the same age or younger targets. Using hippocampo-septal slices the present experiments show that this failure is due to an inability to recognise the glial pathway of the fimbria, even when this is of a younger age. However, the older hippocampal neurons retain the ability to grow axons into septal target tissue when they are placed in direct contact with it. This exactly mirrors the inability of cut central axons to regenerate along their previous fibre pathways while they retain their ability to reinnervate neuropil.