Treatment with an anticoagulant (AC) or acetylsalicylic acid (ASA), chosen at random, was given to 241 patients with symptoms of carotid transient attacks of ischemia, some of whom recovered completely within 24 hours (TIA) while the others had slight residual symptoms (TIA-IR). Cerebral infarction was recorded in 4 patients in each of these treatment groups during a mean follow-up period of 20 months. The incidences of TIA and TIA-IR were also similar in the two groups. Severe hemorrhage occurred more often in the AC group, whereas other side reactions, including gastrointestinal disorders, were more common in the ASA group. Recurrent cerebral ischemic events were significantly more common among the patients that had had greater than or equal to 2 TIAs in the 14 days immediately preceding randomization, and in those with a history of CVS symptoms more than 14 days before randomization, or those with a carotid bruits. In the group experiencing greater than or equal to 2 TIAs in the 14 days prior to randomization the incidence of recurrent cerebral ischemic events was the same for the two types of treatment.