A multicenter comparative trial was conducted in patients with transient ischemic attacks (TIA) to study the preventive capacity of a combination of acetylsalicylic acid and dipyridamol (1,050 mg + 150 mg/day - group A) and of pentoxifylline (1,200 mg/day - group P) in the reduction of morbidity rates. Sixty-six patients, 36 on A and 30 on P, were evaluated. There was no statistically significant difference between both groups as regards age, sex, blood pressure, localisation of TIA and incidence of risk factors. Incidence of new ischemic events during a one year follow up period in the A-group was 28% compared to 10% in the P-group, this difference being statistically significant in favour of P (p less than 0.05). Stroke incidence was similar in both groups but distinctly lower (4.5%) than the natural frequency in TIA.