1. Clonidine was withdrawn acutely in five hypertensive patients with a documented blood pressure over-shoot after previous temporary cessation of treatment.
2. In all patients a severe rise of systolic and diastolic blood pressure was seen (average 67/58 mmHg). This was accompanied by a number of ‘withdrawal symptoms’, e.g. restlessness, tremor, headaches and nausea.
3. Catecholamines in urine rose from 32 μg/l to 112 μg/l (001 < P < 0.02) and in arterial blood from 0.52 μg/l to 1.0 μg/l (not significant).
4. The crisis could be reversed acutely by α- and β-adrenergic blockade.
5. Catecholamine depletion with reserpine before the withdrawal of clonidine seemed to reduce the blood pressure rise and the withdrawal symptoms.