Bulk endocytosis in central nerve terminals is activated by strong stimulation, however the speed at which it is initiated and for how long it persists is still a matter of debate. To resolve this issue we performed a characterisation of bulk endocytic retrieval using a range of different stimulation paradigms. Bulk endocytosis was monitored by either the loading of the fluorescent dyes FM2-10 and FM1-43, uptake of tetramethyrhodamine-dextran (40 kDa) or morphological analysis of uptake of the fluid phase marker horse radish peroxidase. When neuronal cultures were subjected to mild stimulation (200 action potentials at 10 Hz) bulk endocytosis was not observed using any of our assay systems. However when more intense trains of action potentials (400 or 800 action potentials at 40 Hz and 80 Hz respectively) or elevated KCl were applied to neurons, bulk endocytosis was activated. Importantly bulk endocytosis ceased on termination of stimulation, whereas a single synaptic vesicle pathway persisted. Thus bulk endocytosis is a fast triggered event that occurs only during strong stimulation and provides the nerve terminal with an appropriate mechanism to meet the demands of synaptic vesicle retrieval during periods of intense synaptic vesicle exocytosis.