Charybdotoxin is a new member of the toxin family that includes dendrotoxin I and MCD and blocks dendrotoxin-sensitive, voltage activated K+ channels: H. Schweitz, J. N. Bidard, C. E. Stansfeld,1,2L. Fagni,1P. Maes3 and M. Lazdunski. (Centre de Biochimie du Centre National de la Recherche Scientifique, Parc Valrose, 06034, Nice, Cedex, France, 1Laboratoire d'Etude des Régulations Physiologiques, 23 rue Becquerel, 67087 Strasbourg, France, 2(Present address:) MRC Neuropharmacology Research Group, Department of Pharmacology, University College, Gower Street, London WC1E 6BT, U.K., and 3Institut Pasteur de Lille, 1 rue du Professeur Calmette, 59019 Lille, France)