ALDOSTERONE stimulates Na transport across the renal tubule and this effect is also seen in 'model' epithelia such as amphibian urinary bladder, skin and colon1-3. This hormone is thought to act by inducing the formation of proteins through nuclear transcription4. Their nature and actions are unknown but it has been suggested that one such protein may act like a 'permease' and increase the permeability of the apical side of the epithelial cells or they could stimulate the activity of the Na transport pump. Goodman et al.5, have suggested that "some key enzyme" which increases the turnover of fatty acids may be involved and this could be phospholipase. We report here the identification of phospholipase A in toad bladder and frog skin epithelial cells and in their incubation media. Mepacrine, an inhibitor of phospholipase A, blocked the response to aldosterone on Na transport.