Cystic fibrosis is associated with defective epithelial sodium chloride and fluid secretion in epithelia. In addition, there is widespread reductions in sialylation of secreted proteins and increases in the sulfation and fuco-sylation of mucus glycoproteins. The major morbidity in the disease is due to the colonization of respiratory epithelia by Pseudomonas. The cystic fibrosis gene (CFTR) is a cyclic AMP activated Cl channel, which when mutated is retained in the endoplasmic reticulum. We postulate that this Cl channel is responsible for effective acidification of the Golgi. In CF cells, we demonstrate the Golgi pH is higher than in normal cells and suggest that the abnormalities in glycoprotein biosynthesis is due to changes in the kinetics of sialyl transferase, a pH sensitive enzyme. Defects in sialylation also result in decreased sialylation of glycolipids and asialogangliosides are potential Pseudomonas receptors.