Symptomatic carotid endarterectomy trials. The possible benefit of carotid endarterectomy in stroke prevention is being evaluated in three major clinical trials. To date, the European Carotid Surgery Trial has randomized 2,200 patients, 30% of whom have a carotid stenosis of greater than 70% appropriate to their symptoms. The North American Symptomatic Carotid Endarterectomy Trial has randomized 1,000 patients, of whom more than half have this severity of appropriate stenosis. Quality control and the evaluation of outcome events in this trial is achieved by a three-tier review, including review by medical and surgical adjudicators who are blinded to the treatment arm of each patient. Baseline characteristics of the patients eligible but not randomized are similar to those of patients who have been randomized. Two percent of the patients randomized to the surgical arm have declined surgery and crossed over to the medical arm, and 3% have elected surgery after randomization to the medical arm. Both of these studies, as well as a Veterans Administration trial, are continuing to randomize patients. 