1. Thin slices (0.2-0.3 mm) of rabbit renal cortex have been incubated in isosmotic oxygenated acetate media at 25 degrees C with or without ouabain (10(-3) M), amiloride (2 x 10(-3) M) or iodoacetamide (10(-3) M). 2. Slices in normal isosmotic 146 mM-sodium-132 mM-acetate media swelled as reported previously (Cooke & Macknight, 1984). This swelling was not prevented by amiloride or by metabolic inhibition. 3. Slices in isosmotic 132 mM-choline-132 mM-acetate media gained much less water and were little affected by ouabain, amiloride or metabolic inhibition. Choline was able to substitute neither for sodium nor for potassium in activating preparations of renal cortical Na+-K+-ATPase in chloride or in acetate media. 4. Slices in isosmotic 20 mM-sodium-132 mM-acetate medium swelled nearly as much as did slices in normal sodium acetate medium. However, this swelling was impaired markedly by amiloride, by ouabain and by metabolic inhibition. 5. There was a direct correlation between medium sodium concentration and slice water content as sodium was increased from 1.25 to 30 mM in 132 mM-acetate media. However, up to a sodium concentration of 10 mM, amiloride (2 x 10(-3) M) completely prevented this increase in water content. 6. Increasing medium amiloride concentration from 10(-5) to 10(-3) M progressively inhibited cellular swelling in 10 mM-sodium-132 mM-acetate medium. It is concluded that, under these experimental conditions, the dominant pathway for hydrogen ion extrusion from the cells was via amiloride-sensitive sodium-hydrogen exchange. 7. The results are discussed in terms of a model which explains cellular swelling in acetate media in terms of (a) non-ionic diffusion of acetic acid across plasma membranes impermeable to the acetate anion, (b) removal from the cells of the hydrogen ion gained with the acetate by amiloride-sensitive sodium-hydrogen counter-transport and (c) subsequent extrusion of sodium from the cell accompanied by potassium uptake via the ouabain-sensitive Na+-K+-ATPase. 8. The results provide evidence for ion movements across the luminal plasma membrane of proximal tubular cells in rabbit renal cortical slices.