A clinical study was made of 480 patients on respiratory intensive care, which is 4.6%, of 10, 390 patients who were admitted to the postanesthetic recovery room for three years from 1976 to 1978 in Seoul National University Hospital(SNUH) The highest age group was the 11 to 20 year old group. Among 480 patients males were 58. 4%, females 41. 6%. The duration of mechanical ventilation was shortest in the open heart surgery group (32.3 hours). Death rates among diseases and types of ventilators are listed. Standard of weaning in mechanical ventilation are discussed. The pulmonary pathophysiologic involvement in critically ill patients are discussed with the literature.