Background Microparticles (MPs) are small phospholipid-containing vesicles that have procoagulant properties. MPs are thought to contribute to the hemostatic potential of plasma. This study investigated the effects of whole blood (WB) hold time and leukoreduction (LR) on the MP profile and hemostatic potential of fresh-frozen plasma (FFP). Study Design and Methods WB units (n = 12) from healthy donors were divided into two pairs and each pair was held at 20 to 24C for 6 or 24 hours. At the designated hold time, 1 unit from the pair was LR while the other unit was not LR. FFP was prepared by standard procedures, aliquoted, and frozen. The MP content was determined by flow cytometry using an absolute count assay and specific labels for red blood cells (CD235a), platelets (CD41), and phosphatidylserine (PS). The hemostatic potential was determined by thrombelastography (TEG) and coagulation factor assays. Results Compared to non-LR-FFP, LR-FFP had significantly lower numbers of MPs, particularly CD41+ MPs and PS-positive MPs (p < 0.03). LR-FFP, compared to non-LR-FFP, had a slower clot formation time (p = 0.002); lower clot strength (p < 0.001); and lower Factor (F)VIII, FXII, and fibrinogen levels (p < 0.01). With longer WB hold time, the TEG profile was unchanged, although FVIII levels were decreased as expected (p < 0.01). On average FFP units met quality requirements. Conclusion LR of WB resulted in lower hemostatic potential of FFP in conjunction with depletion of MPs and coagulation factors. Longer WB hold time did not significantly affect the hemostatic potential of FFP as measured by TEG. Acceptable hemostatic quality was maintained for all FFP processing conditions studied.