1. Blood pressure was monitored continuously in conscious rats with chronic Goldblatt two-kidney, one-clip hypertension.
2. Hypertension was rapidly reversed by removal of the constricting clip and the reversal was complete by 12 h, although structural vascular changes persisted for much longer.
3. Blood pressure in this model of hypertension was not affected by a 15 h infusion of either indomethacin or aprotinin.
4. The pattern of fall in blood pressure after removal of the clip was similar when animals were infused with either indomethacin or aprotinin. Blood pressure at 24 h was normal and did not differ significantly from that of unclipped rats given a glucose infusion.
5. The fall in blood pressure produced by unclipping therefore did not appear to be mediated via the prostaglandin or kallikrein systems.