In this study we characterized the nociceptive response and edema induced by the venom of the scorpion Tityus serrulatus in rats and mice and carried out a preliminary pharmacological investigation of the mechanisms involved in these responses. Intraplantar injection of the venom (1 or 10mug) induced edema and a marked ipsilateral nociceptive response, characterized by thermal and mechanical allodynia and paw licking behaviour. The nociceptive response was inhibited by previous intraperitoneal administration of indomethacin (4mg/kg), dipyrone (200mg/kg), cyproheptadine (10mg/kg) or morphine (5 or 10mg/kg), but not by dexamethasone (1 or 4mg/kg) or promethazine (1 or 5mg/kg). The edema was inhibited by previous treatment with promethazine (5 or 10mg/kg) or cyproheptadine (5 or 10mg/kg), but not by indomethacin (2 or 4mg/kg), dexamethasone (1 or 4mg/kg) or cromolyn (40 or 80mg/kg). Some bioactive amines, including histamine and 5-hydroxytryptamine, were found in the venom in low concentrations. In conclusion, the nociceptive response and edema induced by the venom of T. serrulatus may result from the action of multiple mediators including eicosanoids, histamine and 5-hydroxytryptamine. These results may lead to a better understanding of the host response to potent animal toxins and also give insights into a more rational pharmacological approach to alleviate the intense pain associated with the scorpion envenomation.