Brevenal, a brevetoxin antagonist from Karenia brevis, binds to a previously unreported site on mammalian sodium channels.

•Brevenal competes with brevetoxin for binding at site 5.•A new radiolabeled ligand [3H]-brevenol was produced.•Brevetoxin cannot inhibit binding of [3H]-brevenol.•Ligands selective for other sites do not inhibit [3H]-brevenol binding.•Brevenal binds to a previously unreported site.