Rabphilin belongs to a protein family characterized by two C-terminal C₂ domains that bind calcium and phospholipids and an N-terminal zinc-finger sequence which was identified as a binding partner of Rab3A, a member of the Rab family of GTPases implicated in vesicle docking and fusion reactions in many systems. In C. elegans Rabphilin, although not essential by itself, contributes to release and the deletion of Rabphilin in mouse hippocampal synapses accelerates recovery of depressed synaptic responses. To further clarify the role of Rabphilin in release glutamatergic postsynaptic currents were recorded at neuromuscular junctions of third instar Drosophila melanogaster larvae using two-electrode voltage clamp. In modified HL- 3 physiological saline with 1 mM Ca²⁺ amplitudes of compound EPSCs were reduced from on average -88 nA ± 5 nA in controls to -45 nA ± 3 nA after Rabphilin knock-down in response to action potentials elicited at a frequency of 0,2 Hz. Paired pulse ratio was increased from 1,1 ± 0,4 in controls to 1,5 ± 0,1 in knock-downs. Furthermore in response to a train of action potentials at 10 Hz release decreased monotonically in controls to a steady state level of -59 nA ± 4 nA, whereas in knock-downs release first increased and then decreased to reach a steady state level at -45 nA ± 3 nA. Time course, amplitudes and frequencies of mEJCs were not significantly different. These data suggest that Rabphilin regulates exocytosis of synaptic vesicles in a use-dependent manner.