When cells were incubated in the absence of bicarbonate, the fluid reabsorption of a non-CF epithelium, where the CFTR basal activity is physiological, is 1.28 ± 0.04 μL/h/cm2 (n = 63), while the fluid reabsorption of homozygous p.F508del-HBEC epithelia is significantly higher (p < 0.0001), with an average value of 1.53 ± 0.05 μL/h/cm2 (n = 48). The gene discussed is CFTR; the disease is cystic fibrosis.