Here analized the chest physiologic changes caused by various degrees of spontaneous pneumothorax in 77 patients admitted in Pusan National University Hospital from Jan. 1991 to Aug.1992. The results were summarized as follow: 1. There were 59 patients of primary spontaneous pneumothorax and 18 of secondary spontaneous pneumothorax. 2. The intrapleural pressure risings were paralled to the increasing sizes of pneumothorax, especiallythe intrapleural pressure changes were significant in large pneumothorax. In the secondary spontaneous pneumothoraces the intrapleural pressure were relatively higher than primary in the same sizes of pneumothorax. 3. The intensity of chest pain was paralled to the increasing sizes and intrapleural pressures of the pneumothorax, but the degrees of dyspnea had no linear interrelationship. 4. The pulse rate, cardiac output, and arterial PO2 started to change from positive intrapleural pressure, and significant changes were noted between 6 to 9 mmHg of intrapleural pressure. But the arterial PCO2 changes had no interrelationship to the degrees of pneumothorax.