The pilocarpine sweat test, and in vivo assessment of CFTR function via nasal potential difference or intestinal current measurement are important tools to confirm the diagnosis of CF in subjects with suggestive symptoms. Since these tests reflect CFTR function and thus relate to the basic disease process in CF, changes in these parameters are also being used to assess the pharmacologic effect of compounds aimed at restoring CFTR function. However, longitudinal data proving that changes in these measurements are associated with meaningful clinical improvements in the course of disease in CF patients are needed. Consequently, many CF clinical investigators need to be facile with these existing methods to measure CFTR-related outcomes. This introduction sets the stage for more in-depth discussion of existing strategies to measure changes in CFTR function generated by gene therapy or small molecule modulators of CFTR function such as correctors and potentiators. It is hoped that lessons learned through the use of these measures will inform the future development of other robust methods to assess novel therapeutic strategies uncovered by basic scientists.