Characteristics of the lung inflation and deflation reflexes were measured at various temperatrues on the cervical vagi in five anesthetized mongrel dogs. Nerve temperature was maintained at the body temperature, and $2-14^{circ}C$ with $2^{circ}C$ apart using a specially designed automated vagal cooling apparatus with an accuracy to within ${pm}0.1^{circ}C$ at each temperature. The inflation reflex was blocked abruptly at $8-10^{circ}C$. The deflation reflex started weakened at $14^{circ}C$, thereafter showed a gradual blockade with the temperature decreased with a substantial variance among the animals. It was approximately 75% blocked at $2-6^{circ}C$. These differences in temperature characteristics made it hard to differentiate the deflation reflex from the inflation reflex. In one animal, however, the inflation reflex was completely blocked with the deflation reflex almost alive at $6-8^{circ}C$. This suegests that differential cold blockade of the vagal reflexes can be done only in selected subjects. Fur- thermore, the fact that these two reflexes were blocked at different temperatures may be due to the differences in the nerve fiber size and the changes in the conduction velocity with temperature.