An agonist-induced expression of CD62P by flow cytometry analysis for evaluating platelet functional reactivity has some disadvantages. We investigated the usefulness of platelet parameters by ADVIA 120 to predict an agonist-induced expression of CD62P in stored platelets. The CD62P expression by flow cytometry and the platelet parameters by ADVIA 120 were studied in samples from 27 platelet pheresis products. Delta (Delta) values were calculated as the degree of change of the platelet parameters studied with or without adenosine 5'-diphosphate sodium (ADP) stimulation. The CD62P expression of the ADP-activated platelets were correlated with the Delta platelet count (r=0.517) in the short-term storage group (within 10 hr from preparation), with the platelet component distribution width (PCDW) without ADP (r=-0.744) and the DeltaPCDW (r=-0.755) in the long-term storage group (after 10 hr from preparation). Therefore, the delta values of platelet parameters on ADVIA 120 analysis in platelets between with and without ADP stimulation could be useful as a simple predictor for the functional reactivity of stored platelets.