Clearance of citric acid under basal conditions in dogs was less than 1 ml/minute. Its clearance was markedly elevated after administration of bicarbonate. Its rise in 7 experiments on 5 of 9 dogs occurred when the calculated filtered load of citrate was less than in the control. This result shows that there was less tubular absorption of citrate. A comparable rise in clearance of citrate followed the ingestion of citric acid but there was a marked increase in the filtered load of citrate and in the quantity absorbed by the tubule. Ascorbic acid did not interfere with absorption of citrate. Elevation of K clearance by administration of K did not increase the clearance of citrate.