Recent work has demonstrated that the geometry (size, shape) of the human ear canal leads to a sound field, at high frequencies, that varies within the canal in a complicated fashion. In particular, the eardrum terminates the ear canal at a rather sharp angle, and significant variations of sound pressure (over 15 dB) arise over the eardrum surface above 10 kHz. The implications of these observations, as they apply to several aspects of hearing research, will be discussed, utilizing a three-dimensional horn equation approach that has been developed. Knowledge of the sound pressure distribution within the ear canal is important in the extension of audiometry to high frequencies, and for guiding the development of hearing aids. Studies of auditory processes that use a reference microphone in the ear canal become increasingly sensitive to microphone location as higher frequencies are used; estimates of the errors of reproducibility are given. Present acoustic network models of the middle ear assume a uniform sound pressure at the eardrum; possible ways of handling a non-uniform pressure distribution are discussed.