During continuous infusion of ethacrynic acid in dogs, changes in glomerular filtration rate (GFR) andPco2at constant plasma bicarbonate concentration (PHCO3) alter bicarbonate and chloride reabsorption in a ratio of 1: 2. This ratio did not apply whenPHCO3was raised by bicarbonate loading in 11 anaesthetized volume‐expanded dogs. A rise inPHCO3from 30 to 54 mM at constantPco2and GFR reduced sodium reabsorption during ethacrynic acid infusion from 3586 ± 725 to 2449 ± 403 μmol min‐1. Bicarbonate and chloride reabsorption were reduced in a ratio of 1: 10. When plasma pH was restored from 7.8 to 7.5 by raisingPco2, the inhibitory effect on chloride reabsorption was halved. At constant plasma pH 7.5 a rise inPHCO3from 20 to 30 mM reduced chloride reabsorption by 20%. A further 30% inhibition was caused by raisingPHCO3from 30 to 54 mM. Bicarbonate reabsorption was highest atPHCO354 suggesting a large capacity for bicarbonate reabsorption ifPHCO3is raised at constant plasma pH 7.5. Water and NaCI reabsorption remaining during ethacrynic acid infusion is almost equally inhibited by alkalosis and by an osmotic effect of unreabsorbed