The kidney expresses two H,K‐ATPase isoforms in the collecting duct, HKα1 or HKα2, that function to transport potassium (K) in exchange for protons, particularly in states of K depletion. However, loss of either HKα1 or HKα2 H,K‐ATPase isoforms did not significantly effect either urinary K excretion or systemic acid‐base balance in mice (Spicer et al. J Biol Chem. 2000 275(28); Meneton et al. J Clin Invest. 1998 101(3)). Because another isoform is present in these single knockout animals, we hypothesized that the H,K‐ATPases compensated for each other. To test this hypothesis, the effect of dietary K depletion on renal electrolyte and acid‐base handling was evaluated in double‐knockout mice lacking both HKα1 or HKα2 (HKα1,2−/‐). Surprisingly, HKα1,2−/− mice efficiently conserved urinary K. However, the HKα1,2−/− mice excreted significantly more urinary titratable acid and ammonium, sodium (Na) and chloride (Cl) with no apparent change in blood Na, Cl, pH, or HCO3. With K depletion, HKα1,2−/− mice retained more urinary Na than wild type mice. The evidence suggests that renal H,K‐ATPases may not play an essential role in net renal K conservation. Instead, the pumps may participate directly or indirectly in both Na and acid‐base transport by the kidney.These studies were supported by an NIH grant (RO1‐DK‐049750).