In this work we have demonstrated the direct neurotoxic e ect of Prasiola crispa methanolic extract at cockroach neuromuscular junctions. At in vivo cockroach neuromuscular preparations the extract induced a progressive and irreversible neuromuscular blockade, which was preceded by an increase in the muscular tonus with the appearance of spontaneous twitches. e previous application of chloral hydrate, a n-methyl-d-aspartate receptor blocker, increased the time to blockade of the muscle twitches by 50%, whereas it extinguished both the previous increase of tonus and the appearance of spontaneous twitches, before the onset of neuromuscular blockade. Together, these results suggest that P. crispa extract induced an insecticide activity by acting mainly at insect neuromuscular junctions. erefore, the NMDA receptors must be the target of this pharmacological interaction. A further phytochemical and pharmacological investigation will increase the knowledge about the cellular and molecular aspects of P. crispa insecticide e ect.