. The effect of intra-arterial prostaglandin E1 (PGE1) infusion on urinary kallikrein, sodium, potassium and water excretion was studied in normal anaesthetized dogs. 2. Infusion of PGE1 caused a dose-related increase in urinary excretion of kallikrein, sodium, potassium and water as well as an increase in renal blood flow (R.B.F.) and a fall in urinary osmolality and renal vascular resistance. 3. The changes occurred in the absence of appreciable changes in inulin clearance (Cin), arterial blood pressure, haematocrit, and plasma sodium and potassium concentrations. 4. The increased urinary kallikrein excretion correlated positively with the natriuresis, diuresis and kaliuresis and the increase in renal blood flow, but negatively with the urinary osmolality and renal vascular resistance. 5. It is concluded that renal kallikrein is involved in the renal response to arterial infusion of PGE1.