The purpose of this clinical study was to evaluate prospectively electrolyte disturbances in elderly patients with severe diarrhea due to cholera. A total of 20 adult (Group I; < 60 yr) and 22 elderly (Group II; 260 yr) patients were studied. In all patients, extracellular fluid (ECF) volume reexpansion was achieved with normal saline at 50 mL/kg per hour. Once a diuresis of 40 mL/h was achieved intravenous therapy was discontinued and patients ECF volumes were reexpanded orally with a polyelectrolyte solution. Blood and urine samples were obtained on admission, at the time when adequate diuresis ensued, and after 12 h of oral ECF volume reexpansion. On admission, both groups had severe ECF volume contraction but only mild increases in osmolality (308 ± 12 and 310 ± 13 mosmol/kg for Groups I and II respectively; P = NS). Acidemia (pH) was equally severe in both (Group I: 7.13 ± 0.11; Group II: 7.11 ± 0.09; P = NS) and the anion gap was comparably increased in both groups (30 ± 8 and 26 ± 7 mmol/L for Groups I and II respectively; P = NS). None of the patients was hypokalemic at the time of admission (Group I: 4.3 ± 0.5 mmol/L; Group II: 4.5 ± 0.5 mmol/L; P = NS). Adequate diuresis was achieved at 2.0 ± 0.7 h in both groups. At the end of the rapid ECF volume reexpansion phase, the anion gap normalized in both groups (Group I: 15.6 ± 3.7 mmol/L; Group II: 14.4 ± 2.8 mmol/L; P = NS) and serum potassium concentrations remained normal (Group I: 4.4 ± 0.4 mmol/L; Group II: 4.1 ± 0.4 mmol/L; P = NS). We conclude that use of aggressive intravenous hydration with normal saline followed by oral ECF volume reexpansion allows prompt correction of electrolyte abnormalities in adult and elderly patients with severe diarrhea as a result of cholera.