Recent studies of mutations of Drosophila proteins implicated in synaptic transmission have yielded new insights into the roles of these proteins and the pathways in which they function. Analysis of mutant embryos lacking syntaxin or synaptobrevin suggests that these proteins perform distinct functions after vesicle docking with the presynaptic membrane. In addition, characterization of Drosophila endocytotic mutants provides in vivo evidence for the presence of different endocytotic pathways at a single synapse.