In Brazil, some snakes of the family Colubridae usually regarded as not venomous, are responsable by serious and even so fatal accidents. Some opisthoglyphous snakes that occur in southern Brazil. as Philodrias olfersii (Lichtenstein, 1823), Boiruna maculata (Boulenger, 1896), Phalotris lemniscatus trilineatus Boulenger. 1889 and Thamnodynastes strigatus (Günther, 1858) deserve greatest attention because they have already caused human envenomation as reported by many authors (Hoge, 1952; Lema, 1978a; Salomao & Di-Bernardo, 1995; Santos-Costa et al., in press). There is at least one record of a fatal accident caused by Philodryas olfersii (Salomao & Di-Bernardo, 1995) and many or her records of serious accidents with the patients showing edema. pain and enlarged axillary lymphnodes (Nickerson & Henderson, 1976; Silva & Buononato, 1984: David & Ineich, 1999). Phalotris lemniscatus trilineatus, a fossorial snake, deserves attention by the gravity of its envenomalion, which may causes hemorrhagic manifestations, local pain, paresthesia and acute renal failure (Lema, 1978b).