Snake venoms are complex mixtures of bioactive agents with diverse pharmacological activities against a wide range of physiological targets. Many of these agents are complex chemicals which have toxic effects upon the cells and cellular mechanisms that they target, and in some snakes the toxicity is sufficient to be extremely harmful to man. Understanding the composition and activities of different snake venoms forearms clinicians with a knowledge of the underlying physiological changes responsible for clinical envenomation syndromes. In some cases this knowledge may enable presumptive identification of the biting species and early selection of the most appropriate antivenom.