The effect of ethyl apovincaminate (RGH-4405, Cavinton) on the cerebral and systemic circulations has been studied in detail in ten cases of cerebrovascular disease. 10 mg doses of Cavinton were given as infusion within 4-6 min; circulatory tests were carried out prior to administration of the drug and 3-6 min after. The principal results showed the following: On Cavinton cerebral vascular resistance was strongly reduced, while cerebral fraction of cardiac output significantly increased. On acute effect of the drug arterial mean pressure slightly decreased but cerebral blood flow nevertheless increased in general. Total vascular resistance also decreased but this decrease was less marked than that registered in cerebral vascular resistance.