Physicians must continue to contribute to the safety, efficiency, and comfort of air travel. Three principles help to determine whether a person is fit to fly as a passenger: there must be no interference with the supply of oxygen to his lungs, the mechanical expansion of gases in his body must be unobstructed, and he must not affect adversely the sensibilities, security, and health of his fellow passengers. The frequency of airsickness and ear trouble is 5 to 10 times as great in children under 5 years as in adults. A woman during the ninth month of gestation must present a certificate, signed by her physician, stating that she will not deliver for at least 72 hours. Antiemetics, nasal vasoconstrictors, and oxygen are effective in combating nausea, preventing pain from ears and sinuses during descent, and alleviating true air hunger. Persons who have recently undergone enteric surgery must be considered carefully because of the effects of possible sudden decompression upon gases in the body. Aviation medicine has developed into a specialty, but prospective passengers generally turn to the physician in general practice. He must therefore be prepared to answer his patients' queries.