Upon exocytosis, synaptic vesicle proteins are released into the plasma membrane and have to be retrieved by compensatory endocytosis. When green fluorescent protein-labeled versions of the vesicle proteins synaptobrevin-2 and synaptotagmin-1 are overexpressed in rat hippocampal neurons, up to 30% are found on axonal membranes under resting conditions. To test whether and to what extent these plasma membrane-stranded proteins participate in exo-endocytic cycling, a new proteolytic approach was used to visualize the fate of newly exocytosed proteins separately from that of the plasma membrane-stranded ones. We found that both pools were mixed and that endocytosed vesicles were largely composed of previously stranded molecules. The degree of nonidentity of vesicular proteins exo- and endocytosed depended on stimulus duration. By using an antibody to the external domain of synaptotagmin-1, we estimated that under physiological conditions a few percent of vesicular proteins were located near the active zone, from where they were preferentially recycled upon stimulation.