The authors present their experience with SNP as hypotensive drug in surgery at cerebral aneurysms. They stress the effectiveness of SNP which they use to control deep hypotensive in 22 cases. SNP induces hypotensive in few minutes, without depressing myocardial and renal functions. The authors present also some criteria at selection of patients (to be treated with SNP during surgery) and stress the importance of monitoring blood gases during SNP hypotensive, especially te pO2 arteriovenous gradient. Using SNP at the recommended doses, and hydroxycobalamin as preventive treatment, no CN- toxicity was noted. The authors think SNP is the drug of choice for inducing deep hypotension in neurosurgery.