The heterogeneous assemblage of advanced snakes currently referred to the family Colubridae are generally considered non-venomous, but there have been several cases of fatal human envenomations by Dispholidus typus (boomslang; Pope, 1958), Thelotornis capensis (formerly T. kirtlandii; twig or bird snake; FitzSimons and Smith, 1958) and Rhabdophis tigrinus (yamakagashi; Mittleman and Goris, 1976; Ogawa and Sawai, 1986; Nomura et al., 1989); the South American colubrid Philodryas olfersii has also been implicated in cases of severe and fatal envenomations (SalomaÄ o and di-Bernardo, 1995; de Araujo and dos Santos, 1997). The high potency and complex nature of these venoms suggest that colubrid venoms may contain compounds with some similarities to front-fanged snakes' venoms, but because the elapids and viperids are distantly related to the family Colubridae, similar activities in colubrid venoms are likely to show novel structural and/or speci®city motifs.