SNP given by intravenous drip has been used to control hypertensive crisis since 1929. Its rapid action makes it suitable for controlled hypotension during general anesthesia. Experience of its use in three cases is described, which undergoing surgery for A-com aneurysm. The results are as follows: 1) The fall in MAP produced by the SNP was directly proportional to the doses of the infusion. (P<0. 01). 2) Increased doses of the SNP caused further rise in pulse rate, but not occurred tachycardia. (P<0.05). 3) The CVP by the SNP decreased consistantly. (P<0.05). 4) When SNP 4ug/kg/min was administered, 2 cases of respiratory acidoses and one case of mild metabolic acidosis were noticed. 5) No CN toxicity was seen, and recovery to normal level of blood pressure was noticed.