Résumé : A study of patients to develop the significance of the role of the blood platelets in the recurrence of transient cerebral ischemic attacks in patients with cerebral atheromatous, develop the effectiveness of dipyridamole in the prophylactic therapeutic regimen. In the group treated with dipyridamole, a 76.3% clinical improvement was recorded (mean increases of 11.2 ml/min. and 11.4 ml/min. of the cerebral hemispheric flows), 15.8% of cases stabilized (mean increases of 1.7 ml/min. and 1.2 ml/min.) and 7.9% failures (mean decreases of 10.4 ml/min. and 14.3 ml/min.) of these same flows. The cerebrography with xenon133 inhaled as well as the platelet tests used, constitute unfailing means of diagnosing and monitoring the clinical development.