Na, K and Cl levels and pH were determined in 26 samples of nasal secretum and plasma obtained from orally intubated intensive care unit patients. In nasal secretum K and Cl were higher and Na lower than in plasma: pH was higher in secretum than in plasma, probably because of the fall of CO2, which freely diffuses to the air. The epithelial activities of lowering pH, secreting K, and reabsorbing Na appeared closely linked together. The chloride difference (DCl) probably balanced the decrease of other anions, such as bicarbonate. Finally, some influences of plasmatic values on ion active transport rates may be hypothesized on the ground of the correlations of chloride and potassium values in nasal secretion and plasma.