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Platelet microparticles (PMPs) are highly procoagulant and might therefore be important in the pathogenesis of arterial thrombotic diseases. The aim of this study was to determine plasma levels of PMPs in survivors of myocardial infarction (MI) and their relation to activation of primary (sCD40L) and secondary (thrombin-antithrombin (TAT) complexes) haemostasis. An observational, population-based case control study was conducted in 61 MI patients 1-4 years after the MI and 61 age-matched and sex-matched healthy controls. PMPs were quantified using an immunoassay that discriminates between small and large PMPs. MI patients had significantly higher total PMPs (314.3 µg/L, 273.1-361.4 µg/L versus 225.8 µg/L, 168.8-273.1 µg/L, p = 0.009) (geometric mean and 95% CI) and larger PMPs (181.3 µg/L, 160.7-204.3 µg/L versus 134.3 µg/L, 104.6-174.9 µg/L) than controls. The differences between groups remained significant after adjustments for use of cardiovascular drugs, body mass index, blood pressure and serum lipids, but were weakened when smoking was included in the analysis. Multiple regression analysis revealed a significant independent association between large PMPs and plasma TAT and soluble CD40 ligand (sCD40L) in MI patients, but not in healthy controls. The independent association between large PMPs and thrombin generation supports the concept that formation of PMPs is important for increased coagulation activation in MI patients. [ABSTRACT FROM AUTHOR]