 For each perfusion condition, a steady-state recording is obtained. The recording lasts at least one minute for Solution 1 and for three minutes for Solutions 2, 3, and 4 prior to proceeding to the next solution within the sequence. Solution 5 is perfused for a minimum of one minute, and confirms retention of ATP-activated Clˉ secretion in both CF and non-CF individuals. Several readings are obtained for data analysis, and then all nasal P.D. tracings are scored by investigators. 