In a previous communication1 the constant presence of air was noted in the coronary arteries of guinea-pigs dead of air embolism induced by intratracheal insufflation of air. Subsequently it was determined to ascertain the effect of air injected directly into the coronary arteries of dogs. The following technic was used on thirty-five dogs: An incision was made in the left third or fourth intercostal space in its ventral fourth, the adjacent ribs were retracted, and the heart was exposed by a vertical incision in the pericardial sac. Air was introduced into the coronary arteries through a fine needle attached to a syringe. Intratracheal insufflation of ether and artificial respiration were maintained throughout the experiment. Four series of experiments were performed. In the first, air injections were made into the left coronary artery or either or both of its branches. In the second, injections were made into both coronary arteries.