The purpose of the study is to develop new biomarkers for studies of cystic fibrosis (CF). Defects in the gene encoding Cystic Fibrosis Transmembrane Regulator (CFTR) cause CF, an autosomal recessive disorder affecting mainly the pulmonary and digestive tract, leading to early death largely due to progressive loss of pulmonary function. In vitro experiments show that quercetin - a dietary supplement with a well-established safety profile for human use, including clinical trials in a variety of disorders encompassing cancer, heart disease, and as an anti-inflammatory agent - induces activation of CFTR. The nasal potential difference (NPD) test is a measurement of voltage across the nasal membrane and as a fundamental biomarker for CFTR activity in vivo. The NPD is a useful, well-established tool in CF research to determine both diagnoses as well as to measure the effect of new therapies. In vitro experiments show that quercetin induces activation of CFTR additive to that seen with current NPD reagents. In addition, it activates rescued mutant CFTR in vitro (∆F508 CFTR the most common cause of CF), whereas conventional agonists do not. Preliminary in vivo experiments mirrored these results and show that quercetin activates CFTR in human (n=12) NPD tests. Importantly, quercetin perfusion was well-tolerated by a validated sinus questionnaire and physician assessed nasal examination rating. These studies provide strong support for use of quercetin as potentiator of CFTR Cl- channel function by nasal administration. By adding quercetin to the sequence of perfusion solutions for NPD, the investigators may be better suited to detect ∆F508 CFTR activity of rescued mutant protein in the CF patient population.