Pulmonary function is the determinant of blood gas tension. However, Acid-Base disturbances can also alter partial pressures of oxygen and carbon dioxide in arterial blood. During respiratory acidosis PO2 will be lowered and reverse changes will be produced during respiratory alkalosis. On the other hand, in metabolic acidosis PO2 will be elevated and PCO2 will be lowered by the respiratory compensation, and reverse response will be induced in metabolic alkalosis. Urinary gas tension has many influencing factors than arterial blood and difficult to estimate the tendency of its alterations. Urinary PO2 and PCO2 are not always identical level as venous blood. It is to be altered by blood gas tension, flow rate of urine, metabolic rate of kidney, and Acid-Base status of blood. Particularly countercurrent exchange of oxygen and carbon dioxide in the renal medulla will make larger alteration of gas tension than venous blood. After induction of Acid-Base disturbances [disturbances] arterial and urinary PCO2, PO2, urinary volume, and osmolarity were determined in dogs, and the relationships between arterial and urinary PCO2 , PO2 Acid-Base disturbances, urinary volume, and osmolarity were investigated. 1. During the acute Metabolic and Respiratory disturbances urinary pH did not respond on respiratory origin. However, there were immediate urinary response in pH on metabolic origin. 2. Urinary PO2, PCO2, did not always follow arterial or venous gas tension and Acid-Base disturbance. Urinary PCO2, correlate well with the urinary volume. The larger the urinary volume, PCO2 lowered to the venous level. The smaller the urinary volume, urinary PCO2 tends to be higher. However urinary PO2 did not have any particular correlation with urinary volume. 3. Correlation between urinary PCO2 and PO2 were inversely proportional to arterial blood. Differences of PCO2 between arterial blood and urine also did not have any particular correlation with urinary volume. This may suggest that changes on blood gas tensions can influence on urinary PCO2. 4. There were eminent clear inverse correlation between urinary PCO2 and osmolar concentrations of urine. Above results strongly suggest that partial pressure of gas in urine primarily depend upon counter-current exchanges in renal medullary tissues. [KTCS 1983;2:213-220]