We report on four patients with hemodynamic brain infarction and pathological circadian blood pressure patterns with nocturnal hypotension which gave rise to a prolonged disturbance of the blood-brain barrier. Besides at least one severe stenosis of the internal carotid artery, there was an untreated chronic arterial hypertension and a pathologically reduced vasomotor reactivity after CO2 stimulation in all patients. The 24-h blood pressure monitoring then carried out showed a distinctly pathological circadian profile with hypertensive day values and nocturnal hypotension with minimum values of 95/50 mm Hg. The range of variation between day and night values was significantly raised (systolic: 20% +/- 2.15%; diastolic: 22.9% +/- 2.58%) compared to patients with essential hypertension as well as normotensive subjects (P < 0.01), and was in excess of 40% in the individual case. There was a slow recovery of the blood-brain barrier after drug-induced normalization of the pathological circadian blood pressure profile. We conclude that the registration of circadian blood pressure patterns may be of prognostic and therapeutic relevance. It may also contribute to further clarification of the pathophysiological significance of blood pressure variability for the development of brain infarction.