Aircraft reconnaissance observations from the eye of unusually deep typhoons (minimum sea level pressure ≤900 mb) indicate that temperature and moisture conditions in the layer between the surface and 700 mb usually undergo rather large changes at about the time of lowest pressure. Abnormally warm, dry soundings are found almost exclusively during the period that the sea level pressure is falling rapidly. Following the time of lowest pressure, the soundings are quite moist in most instances and lapse rates are very close to the moist adiabatic rate. The size of the eye also shows systematic changes between the deepening and filling stages of the storm. The eye usually decreases in size as the storm deepens with the minimum value occurring near the time of lowest pressure. Cloud data for the eye indicate quite variable conditions and fail to show differences between the deepening and filling stages of the type which might have been expected from the observed changes in temperature and moisture within the eye. The temperature changes in the surface to 700-mb layer offer a relatively small contribution to the observed changes in sea level pressure in tropical cyclones. Although observations are not available for the upper tropospheric portions of the eye, some qualitative statements can be made in regard to the temperature changes in this upper layer by considering the observed temperature changes in the lower layer along with the changes in sea level pressure.