Three features distinguish CF from controls: 1) higher basal PD, reflecting enhanced Na+ transport secondary to relative Cl- impermeability 2) greater inhibition of PD after nasal perfusion with amiloride, a Na+ channel inhibitor, and 3) little or no change in change of Cl- transport in response to perfusion with a Cl--free solution along with isoproteronol, (which reflects an absence of CFTR-mediated Cl- secretion). The gene discussed is CFTR; the disease is cystic fibrosis.