Forty-seven patients with hypertension and/or cerebrovascular disease were examined by an acute controlled hypotension test. This was performed by intravenous administration of the ganglionic blocking agent pentholonium and head-up tilting on a pivoted table with observation of the clinical neurological state and simultaneous EEG recording. Blood pressure was reduced by approximately 55% and brought to the point where signs of general cerebral ischaemia developed. By tilting back to horizontal the blood pressure returned to near the normal level. No change in focal neurological symptoms or changes in the EEG were observed, and it is concluded that the majority of hypertensive patients with or without previous stroke do tolerate normalization of their blood pressure. Controlled hypotension with tilting seems a simple and valuable test for excluding those few subjects who might not tolerate a blood pressure reduction. Whether EEG monitoring during the test increases the value of the test has not been answered.