A procedure for the isolation of the toxin Tityustoxin VII (TsTX-VII) from Tityus serrulatus scorpion venom and its biochemical characterization is reported. This protein has a Mr = 6,700 - 6,800, eight half-cystine residues accounting for four disulfide bridges and no His. Its N-terminal sequence GHZGYGS ....... characterizes it as a new toxin, able to release glutamic acid and gamma aminobutyric acid from rat brain synaptosomes 'in vitro'. This release was also induced by the whole venom. Tetrodotoxin however blocked the effect of the whole venom but not that of TsTX-VII, thus suggesting that the releasing mechanism by TsTX-VII does not involve Na+ but perhaps K+ or Ca++ channels.41612551263