The analog of cis-tetramethrin with a 2,2-dimethyl-cyclopropyl replacement for the 2-methyl-1-propenyl group, i.e., "methanotetramethrin", is one of the most neuroactive compounds ever described. It is 10(3)- to greater then 10(5)-fold more potent than tetramethrin in inducing repetitive firing following stimulation in a cockroach cercal sensory nerve in vitro, and the repetitive firing is considerably more persistent. Also, it is more toxic to the cockroach and the housefly. The remarkable potency of methanotetramethrin, giving consistent repetitive firing in this nerve assay at 10(-18) M, and the speculation that it may undergo reversible covalent binding via Michael addition indicate that it could be a useful neurophysiological probe and candidate affinity label for the sodium channel.