We recently showed in dogs that there is a close relationship between bicarbonate reabsorption and glomerular filtration rate (GFR). The present studies were designed to confirm these findings in five normal men. Bicarbonate titrations were done after ingesting a low protein diet for one week and were repeated following elevation of GFR 11–29% by high protein diet and dexamethazone ingestion. In every case tubular reabsorption of bicarbonate increased in proportion to the increases in GFR. We conclude that glomerular-tubular balance for bicarbonate reabsorption is a characteristic of human, as well as canine kidneys.