SummaryThe role of platelets in the thrombogenic process is reviewed in the light of recent experimental data. There is good evidence that intimal lesions are initiating a process which represents both haemostasisandthrombogenesis, by exposing subendothelial sites attractive to circulating platelets. In turn, activated and aggregated platelets may induce pathological modifications of the vascular wall, especially proliferation of smooth muscle cells. Finally activated (“nasty”) platelets embolize in the microcirculation, and might be responsible for metabolic, toxic and inflammatory lesions in the absence of ischaemia.