Secretion from Duvernoy's gland of the colubrid snakes Malpolon, Spalerosophis, and Thamnophis was obtained by pilocarpine stimulation and tested for lethality and selected enzymatic activities. Pools of secretion from Malpolon and Spalerosophis were fractionated by gel filtration, and several major active fractions were examined. The secretion from Malpolon had an LD50 of 6.5 μg/gm in mice; two lethal fractions with LD50's of 2.75 μg/gm and 4.5 μg/gm were isolated. One of these fractions appears to be a basic phospholipase A with a molecular weight of about 17,000. Spalerosophis had a secretion with an LD50 of 2.75 μg/gm in mice; one main lethal fraction with an LD50 of 2.5 μg/gm was isolated. Secretion from Thamnophis had an LD50 of 33.3 μg/gm; it was not fractionated owing to a paucity of material. At least two of the snake species examined have toxic secretions that may be important during feeding by killing or weakening and helping to subdue the struggling prey.