1. We measured urinary kallikrein (kininogenin) excretion in black and white normotensive subjects during a variety of manipulations of salt and water balance.
2. A large intravenous saline load administered while the subjects were on an unrestricted sodium diet did not significantly change urinary kallikrein activity in either racial group.
3. After several days of dietary sodium restriction both racial groups increased their urinary kallikrein activity. An intravenous water load given then further increased urinary kallikrein activity. White subjects were studied for an additional 24 h period, and urinary kallikrein activity returned to pre-water load values, indicating that the excretion of a water load in sodium-depleted subjects is associated with an increase in kallikrein excretion.
4. Black subjects excreted less kallikrein in the urine than white subjects during the initial 24 h periods of unrestricted dietary sodium intake, but there were no other significant racial differences during the other experimental conditions.