The purpose of this study was to identify effective methods to minimize increases in intracranial pressure(IICP) during endotracheal suction by means of comparing two methods of hyperventi-lation and oxygen supply before and after endotracheal suction. In order to evaluate the effects of these two methods, the ICP during suctioning and the sustained time of I ICP were measured. For hyperventilation, ambu-bagging was done 10 times for 30 seconds with a tidal volume of 800-900ml. For oxygen supply, 100 percent oxygen was supplied for 2 minutes before and after suction. The subjects for this study were 12 neurosurgical patients who had had a subarachnoid bolt inserted for ICP monitoring and they were all on mechanical ventilatory support in a surgical intensive care unit of Seoul National University Hospital from July 1, 1991 to March 31, 1992. In each patient hyperventilation was performed five times and oxygen supply was given five times and intracranial pressures were measured immediately before and every 30 seconds for 15 minutes after suction. For case assignments counterbalancing and repeated measure designs were combined. And so the total number of experiments were sixty for each group. The effects of hyperventilation and oxygen supply on the IICP and the sustained time of IICP after suction were analyzed by t-test. The results of study were as follows 1. There was a significant difference between the two groups in the increased ICP during suction (t=2.49, p=.014). 2. The sustained time of IICP after suctioning in the oxygen supply group was shorter than that in the hyperventilation group(t=2.35, p=.020) In summary, the Increase in the ICP during suction was lower and the time for the ICP to return to the presuction level was shorter in the oxygen supply group as compared to the hyperventilation group. Therefore, oxygen supply can be recommended before and after endotracheal suction.