Platelet turnover is increased when platelets interact with prosthetic surfaces and damaged vessel wall. To determine whether the resulting increase in young platelets is associated with an increased tendency to thrombosis, we induced a state of increased platelet turnover in rabbits by inserting a sterile cannula into the abdominal aorta and tested for platelet thrombogenecity by measuring the deposition of circulating platelets onto a second injury site in the carotid arteries. Platelet half-life was decreased and platelet turnover was increased after the aortic cannulation, although the circulating platelet count remained unchanged. Platelet thrombogenecity determined 20 hr after cannulation was significantly decreased when compared to sham-operated animals. Ear bleeding studies demonstrated that the platelets circulating in cannulated animals were hemostatically less effective than those in sham-operated animals. This effect was intrinsic to the platelet and was associated with a platelet function defect. These data suggest that platelets exposed to a damaged or foreign surface interact with the surface and then circulate in a less reactive state.