Guidelines for appropriate use of hypertonic (3%) saline (HS) for the treatment of hyponatremia are ill-defined. We reviewed each infusion of HS in a 400-bed university hospital over a 1-year period. Of the 14 infusions, the hyponatremia (average serum sodium [Na+] 19.9 +/- 6.7 mEq/L) was chronic in 11 cases and acute in only 3. In only 2 patients were there symptoms possibly attributable to hyponatremia. On the average, more than 5 hours elapsed from the last measured serum Na+ level to the initiation of HS infusion, and the next measured serum Na+ value came more than 6 hours later. HS should be reserved for symptomatically hyponatremic patients, most of whom become acutely hyponatremic. A target level for the serum Na+ should be determined and a time-course for correction set. The infusion should be started promptly and monitored frequently for the effect on the serum Na+ level and patient symptoms.