1. A large dose of oestrogen elevated the blood pressure in male Wistar rats.
2. Plasma renin substrate and renin activity increased significantly but plasma renin concentration was unchanged.
3. The increase in blood pressure induced by oestrogen was significantly reduced by salt loading, plasma renin concentration was suppressed and the increase in plasma renin activity was reduced.
4. The increase in plasma renin activity induced by the increase of plasma renin substrate concentration may play a role in oestrogen-induced elevation of blood pressure.