To study the influence of the measurement of the platelet-monocyte aggregates (PMAs) by using of flow cytometry (FCM). Anticoagulated peripheral venous bloods from nine healthy donors were incubated with a PE-CD14 MAb (monocyte marker) and a FITC-CD42a MAb ( platelet marker) for 20 min and the formations of PMAs were measured by use of FCM. The factors such as fixative, anticoagulant, storage time and temperature were analyzed. The PMAs of citrated whole blood increased with the time elapsed in 6 h after blood drawing when they were stored in the room temperature. The PMAs of each time point showed significant difference (P <0.05). Furthermore, the citrated samples stored in 4℃ caused more PMAs formation. The formation of PMAs did not increase with the time and temperature changed when the whole blood were anticoagulated with K#_2# EDTA or citrate sodium added with 0.5% Paraformaldehyde (PFA). However, both of them can cause the PMAs disaggregate, which may affect the measurement of the PMAs formed in vivo. The citrate sodium may not influence the formation and stability of the PMAs. Measuring the citrated whole blood quickly after drawing the blood appears to reflect closely the PMAs in vivo.