Abstract Platelets release microparticles (PMP) upon activation. Elevated levels of PMP were observed in patients with immune thrombocytopenic purpura (ITP), sometimes associated with a syndrome resembling transient ischemic attack (TIA), suggesting a thrombogenic potential for PMP. To determine if this association applies to TIA and other cerebrovascular accidents (CVA) without ITP, we studied PMP profiles in 71 patients with ischemic CVA: 28 with small vessel CVA (SCVA), either lacunar infarcts or TIA; 24 with large vessel CVA (LCVA); 19 with multiinfarct dementia (MID); 12 with Alzheimer's dementia (AD); and 31 healthy controls. The mean PMP values were: MID = 3.71 ±0.51; SCVA = 3.48 ±0.63; LCVA = 1.97 ±0.28; AD = 1.19 ±0.27; controls = 0.88 ±0.09, (all units × 10 7/mL). PMP values in all groups except AD were significantly above normal (p<0.01). However, the elevation in SCVA was more marked than in LCVA (p<0.01). Administration of the calcium channel blocker, nifedipine, to 11 TIA patients reduced PMP significantly.