The effect of D-aldosterone and dexamethasone on kallikrein release was studied in the isolated rat kidney perfused with modified Krebs-Henseleit buffer. 2. Animals received D-aldosterone or dexamethasone (10 microgram/100 g body weight) daily for 3 days. Their isolated kidneys were then perfused with the same steroids at rates of 2.0-2.5 microgram/min for 30 min. 3. Dexamethasone increased kallikrein release significantly (P less than 0.001) both in urine and in venous outflow. 4. D-Aldosterone had no significant effect on kallikrein release, either in urine or in venous outflow.