In the course of some observations on the blood gases in asthma,1 certain findings indicated significant changes in the circulatory mechanism. Recently there has been an opportunity to make similar studies on two patients with acute laryngeal edema and interesting changes were found in the blood gases and blood reaction. Though the clinical studies have been temporarily abandoned because of a lack of material, the findings in asthma and acute laryngeal edema led to a series of controlled observations on experimental respiratory obstruction in dogs. The problem was to study the effects of partial tracheal obstruction on the blood gases, blood reaction and volume flow. The object of the present article is to report the results of these experiments. METHOD Since asthma is difficult to produce in dogs and the experimental production of laryngeal edema is unsatisfactory, the following technic was employed to produce tracheal obstruction: Dogs of from