The objective of the proposed research project is to study the processes of ventilation of the middle ear and sinuses. The purpose is to obtain knowledge that will have direct application to clinical diagnosis. An approved dosage of Xenon-133, a radioactive gas, is administered to normal subjects by means of a bilateral negative-positive pressure air displacement technique that yields an initial concentration of the gas in the sinus and middle ear cavities. The rate of egress of the gas from the individual cavities is measured using a scintillation camera that is interfaced to a PDR-15 computer. Simultaneously, two small probes (6 mm diameter) are placed at counters. The computer data and the portable equipment data will be directly comparable, so the portable equipment can be assessed for its value in providing reliable rates of egress. Normal rates of ventilation of the mentioned cavities are being determined from the data. Subjects with confirmed pathology of the middle ear or sinuses will then be tested to determine if a desired correlation is obtained in relationship to normal standards. It is hoped that this research will help solve some of the most crucial problems of otology.