Prazosin hydrochloride, a post-synaptic alpha receptor blocking agent, was administered to twelve patients with acute pulmonary oedema due to scorpion sting in order to lower their mean blood pressure (diastolic blood pressure plus one-third of pulse pressure) 10 to 20 mmHg. Following an oral dose (0.125 mg in children and 0.5 mg in adults), clinical improvement was seen in the form of disappearance of apical systolic murmur and pulmonary oedema, a reduction in heart rate observed at the end of the first hour, and maximal improvement seen at the end of the third hour. Chest radiographs showed conspicuous clearing of pulmonary oedema. Electrocardiographs (ECG) showed hypoxic injury patterns such as a Q-wave in lead I and AVL with tented T waves in precordial leads, left anterior hemiblock (LAHB) and acute infarction patterns with subsequent T-wave inversion. The severity of clinical signs and ECG changes increased as the time between the sting and attending hospital lengthened.