The basolateral Na⁺/K⁺ATPase plays a critical role in sodium reabsorption across airway epithelium. Nasal epithelium shows increased Na⁺/K⁺ATPase activity in cystic fibrosis (CF) but Na⁺/K⁺ATPase has not been characterized in human lung epithelium or compared in CF and normal lung. We measured³[H] ouabain binding and Na⁺/K⁺ATPase activity in human tracheal epithelium and compared Na/K ATPase activity in bronchial epithelium in CF and control subjects. In tracheal epithelium Na⁺/K⁺ATPase pumps were abundant and of high³[H] ouabain affinity (Kd 4.7 nM, B_max38 pmol/mg) and Na⁺/K⁺ATPase activity was 55±8 nmol/mg protein/min. Bronchial epithelial Na⁺/K⁺ATPase activity was twofold higher in CF patients than in controls. The increased Na⁺/K⁺ATPase activity may contribute to the increased sodium reabsorption seen in cystic fibrosis.