The temperature-induced paralysis of comatose (comt) mutants of Drosophila is suggestive of a function for N-ethylmaleimide-sensitive fusion factor (NSF) in the CNS. Mutations in the para gene encoding the subunit of the voltage-gated sodium channel also result in a similar phenotype. We show that paralysis in comt flies is activity-dependent, and in the doubly mutant comt para flies comt-like paralysis does not set in until the effects of para are reversed by shifting to permissive temperatures. During recording from the thoracic flight muscles, we observed that comt flies showed a burst of spontaneous activity at restrictive temperature. This has been reported earlier as a unique characteristic of comt paralysis. The comt para double mutant showed this burst of activity not at restrictive but only on shifting back to permissive temperature. The unusual behavior and electrophysiology of the doubly mutant flies reported here indicates a role for NSF in synaptic vesicle cycling.