We report a new type of congenital "secretory diarrhea" in a 9-year-old girl that led to contraction and severe metabolic acidosis in the first weeks of life. Her fecal Na+ concentration was high and the pH alkaline. All known causes of secretory diarrhea were excluded. Our findings indicate a defect in the handling of Na+ and H+ in the distal ileum and colon. Treatment with orally administered Na-K-citrate supplementation has normalized her fluid and electrolyte status and allowed normal growth and psychomotor development, but the diarrhea has persisted.