Water and electrolyte content influences the rheology of respiratory mucus. Nasal secretions can be obtained from almost all patients and may be regarded as a possibly useful model of the electrolyte composition of lower airway secretions that are difficult to collect in most patients. Na, K, and Cl were determined from nasal secretions in 35 ICU patients. We studied the relationship of those values to the patients' water and salt states. Our study indicates that: a) lower K and Cl levels and higher Na levels than those found in plasma are common to both nasal and bronchial secretions; b) variations of electrolyte levels in nasal secretions are interrelated; c) patients with lower values of free-water clearance show lower Na and higher Cl levels in nasal secretions, possibly due to increased epithelial transport; d) the amount of K in nasal secretions appears correlated with its urinary fractional excretion (this could be explained by the variations in intracellular K levels); and e) in hyperchloremic patients, plasma/secretion differences of Na are decreased, possibly due to decreased epithelial transport.