1. Rat kidney extracts obtained at successive stages of a purification procedure, which allows the separation of renin and kallikrein, were used in order to investigate their effect upon urinary excretion of kallikrein, sodium, potassium and water in hyperhydrated rats.
2. Only the purified fraction containing renin reduced kallikrein excretion. The decrease of kallikrein coincided with a considerable increase in sodium, potassium and water excretion.
3. The natriuretic effect of renin extract did not depend on the presence of kallikrein. The injection of a mixture of renin and kallikrein attenuated the effect of renin alone, indicating that both enzymes exert antagonistic actions on the excretion of electrolytes and water by the kidneys.
4. A purified fraction of kidney extract containing no kallikrein and only traces of renin activity, had a stimulatory effect on kallikrein, water and elctrolyte excretion.