Intracellular microelectrode techniques were used together with inhibitors of Na⁺ transport (amiloride) and H⁺ transport (acetazolamide and SITS¹) to identify principal cells and intercalated cells in the outer stripe of the rabbit outer medullary collecting duct. The principal cell (n=9) had a basolateral membrane voltage (V _bl) of −64.7±3.2 mV, a fractional resistance of the apical membrane (fR _a=R _a/R _a+R _bl) of 0.82±0.02, and a K⁺-selective basolateral membrane. Luminal amiloride hyperpolarizedV _bl by 10.3±2.1 mV and increasedfR _a to near unity (n=7). Bath acetazolamide and SITS were without effect on these parameters. The intercalated cell (n=5) had aV _bl of −25.0±3.2 mV, afR _a of 0.99±0.01, and a Cl⁻-selective basolateral membrane. Bath acetazolamide or SITS hyperpolarizedV _bl by 26.4±8.2 mV. Luminal amiloride did not alterV _bl of this cell. The differential effects of the inhibitors also indicate that the principal and intercalated cells are probably not directly coupled electrically.