This article presents an overview of the progress that has been made in recent years in our understanding of the interaction between exercise and platelets in health and disease. Although platelets are important in normal haemostasis, recent evidence emphasises the pivotal role of abnormal platelet function in acute coronary artery diseases, myocardial infarction, unstable angina and stroke. In light of the positive health benefits of exercise, interest has been heightened on the association between exercise and platelet aggregation and function, not only in normal healthy subjects but also in patients. However, the study of exercise effects on blood platelets are highly contentious because of the fact that the analytical methods employed to study platelets are bedevilled by numerous methodological problems. While exercise effects on platelet aggregation and function in healthy individuals have been extensively examined, the evidence reported has been conflicting. Somewhat less contradictory are the results generated from studies in patients with coronary heart disease, as the preponderance of evidence available would strongly suggest that platelet aggregation and function are increased with exercise. Several drugs are known to influence platelet aggregation and function, the most examined among these medications is aspirin (acetylsalicylic acid). However, aspirin appears to be ineffective to attenuate exercise-induced increases in platelet aggregation and activation. Few studies are available on the effect of training on blood platelets and the exact effects of exercise training on platelet activation and function is not as yet known. This lack of information makes further studies particularly important, in order to clarify whether there are favourable effects of exercise training on platelet aggregation and function in health and disease.