Stroke prevention using antiplatelet agents is now a routine part of therapy in patients with transient ischaemic attack (TIA) or stroke. Aspirin (acetylsalicylic acid) is the most widely used agent. Other agents with clinically established efficacy are ticlopidine and dipyridamole.Despite its widespread use, the efficacy of aspirin is modest, being approximately 15 to 18% in major placebo-controlled trials of the prevention of stroke. The optimal antithrombotic dosage of aspirin for stroke prevention has not been established from a direct comparison of dosages in patients with TIA or stroke. At present, the most frequent recommendation is a dosage of between 100 and 300 mg/day. However, it has not been proven whether very low dosages (30 to 50 mg/day) or dosages as high as 1300 mg/day offer slight, marked or no major benefit with regard to the prevention of a first or recurrent stroke. There is some evidence indicating the lack of a relationship between aspirin dosage and gastrointestinal haemorrhages and haemorrhagic stroke, but a relationship does exists between dosage and gastrointestinal symptoms and withdrawals due to adverse effects.Ticlopidine has proven to be more effective than aspirin in reducing the risk of stroke in patients with TIA and stroke. Patients who do not tolerate aspirin because of allergic or gastrointestinal reactions are candidates for ticlopidine. The most commonly used dosage of ticlopidine is 250mg twice a day. A new derivative of ticlopidine, clopidogrel, seems to be as effective as ticlopidine and is free from the most harmful adverse effect of ticlopidine, i.e. neutropenia.Recent data indicate that the combined use of aspirin and dipyridamole has an additive effect in patients with TIA and stroke compared with either drug alone. This combination was stated as being twice as effective as either drug alone in the second European Stroke Prevention Study.Despite encouraging data on new alternatives, aspirin is still the most widely accepted first-line treatment for the secondary prevention of stroke.