Role of aprotinin (kallikrein-kinin synthesis inhibitor) in preventing the cardio-respiratory toxicity induced by Mesobuthus tamulus (BT) venom was evaluated. The effects of BT venom (5 mg/kg) on mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), lung compliance and pulmonary water content were examined. BT venom produced alterations in MAP, HR and RR. The MAP changes were seen as an immediate fall (within 2 s) followed by a rise and subsequent progressive fall. The HR was decreased drastically after venom and never returned to initial value. The respiratory changes were manifested as prolonged apnea with intermittent shallow breathing. The animals died within 30-60 min. In these animals, the lung compliance was decreased as compared to saline treated controls and there was significant increase in pulmonary water content. In aprotinin pre-treated group, there was decrease in MAP, HR and RR within 2 s which returned to pre-venom level within 15 min and remained at that level thereafter. The animals survived for the period of observation (i.e. up to 120 min). The compliance and pulmonary water content in these animals were similar to control animals. The results indicate that aprotinin protects against the BT venom-induced cardio-pulmonary toxicity.