The size of the free space in the nasopharynx is of interest to many specialists in different branches of medicine. Up to now it has not been possible to measure this space. A new method is described which permits the determination of the size of the nasopharynx in measureable and comparable units. The method which has been worked out and tested from the medical point of view is simple, rapid, sparing, not exacting for the patient or surgeon and only requires the simplest equipment, so that it can be used in routine outpatient work. In the interests of more exact measurement it would be necessary to improve the inflatable sacs technically so that the properties and quality correspond to the requirements given on page 313 of the paper. The author would be grateful to make contact with a suitable technical laboratory which could develop and produce such sacs.