The adrenocortical steroid hormone, aldosterone, regulates water and electrolyte transport in the distal tubules and collecting ducts of the nephrons in the kidney. Evidence has accumulated that it participates also in epithelial sodium absorption and potassium excretion in the colon acting via mineralocorticoid receptors. However, it is unclear whether aldosterone, like corticosterone, can be synthetized locally in the gut epithelium. Here we describe for the first time the expression of immunoreactive aldosterone in different sections of the murine gastrointestinal tract, with highest levels in the caecum. If similar findings can be verified in humans, this intestinal aldosterone might not only be of compensatory significance in severe renal failure, but also have a role in inflammatory bowel diseases as well as contributing to the development of salt-related hypertension.