The present invention relates to methods of using compounds of Formula I, wherein R1a, R1b, R2, R3, R4, W, Y, and Z are as described herein, and pharmaceutically acceptable salts thereof. The compounds are potentiators of Cystic Fibrosis Transmembrane conductance Regulator (CFTR). The invention also discloses pharmaceutical compositions comprising the compound, optionally in combination with additional therapeutic agents, and methods of potentiating, in mammals, including humans, CFTR by administration of the compounds. These compounds are useful for the treatment of cystic fibrosis (CF), asthma, bronchiectasis, chronic obstructive pulmonary disease (COPD), constipation, Diabetes mellitus, dry eye disease, pancreatitis, rhinosinusitis, Sj?gren' s Syndrome, and other CFTR associated disorders.