Preliminary data show that following β-adrenergic stimulation, evaporimetry can reliably measure sweat secretion that is: highly reproducible in healthy controls; reduced by 50% in CF obligate heterozygotes; and absent in CF patients carrying severe mutations on both alleles. Further, test- retest experiments suggest good intra-individual reliability. All these features satisfy the required criteria for a biomarker assay that is capable of assessing small increments in CFTR function in vivo in clinical trials designed to assess the effectiveness of correctors and potentiators of CFTR channel activity. Therefore, to provide additional evidence of the value of this novel technique the investigators will determine the accuracy and reliability of evaporimetry to measure Beta-adrenergic induced sweating in subjects with a range of CFTR channel activity.