Cocaine abuse is associated with heightened risk of life-threatening neurological complications such as strokes, seizures, and transient ischemic attacks. We used transcranial Doppler (TCD) sonography, a continuous measure of cerebral blood flow velocity, to better understand the changes in cerebral hemodynamics produced by cocaine administration, which may lead to an increased risk for stroke in cocaine abusers. Heart rate and blood pressure were also measured. Blood flow velocity of seven cocaine abusers was studied during placebo, 10-, 25-, and 50-mg intravenous (i.v.) injections of cocaine. A significant increase in mean and systolic velocity which lasted for about two minutes was observed with all doses of cocaine, with no change in the placebo condition. This increase in systolic velocity indicates that cocaine produces an immediate and brief period of vasoconstriction in large arteries of the brain. The present results elucidate the time course of cocaine's acute cerebrovascular effects and provide a better understanding of etiology of cocaine-related stroke and transient ischemic attacks.