1. Forearm venous plasma noradrenaline, heart rate and intra-arterial blood pressure were measured sequentially during and after upright bicycle exercise in five normotensive and six hypertensive patients.
2. Plasma noradrenaline increased significantly between 4 and 8 min during exercise.
3. On stopping exercise blood pressure and heart rate decreased rapidly whilst plasma noradrenaline increased in each subject to reach a maximum at a median time of 108 s after exercise.
4. Plasma noradrenaline decreased in five of six normotensive patients between the end of exercise and 2 min after exercise performed in the supine position.
5. Evidence in favour of a reflex increase in sympathetic activity after upright exercise is discussed.