Recent studies have shown that axonal growth is disrupted by treatments that block the synthesis of membrane components or their delivery by microtubule-based transport. This implies that a continuous supply of newly synthesized membrane components is necessary to sustain growth. In contrast, no clear consensus has yet been achieved about the site of insertion of new membrane components in the membrane of the growing axon, despite the application of new and refined biophysical and molecular techniques to the study of this issue. Until the site of insertion of new membrane components is resolved, little progress can be made in defining the feedback mechanisms by which the supply of new membrane components is co-ordinated with the demands of growth, particularly in cases where the dynamics of neurite growth change from minute to minute.