A. Platelets in whole blood harvested from SR-BI+/+ (WT, black bar, n=20), SR-BI+/− (gray bar, n=17) and SR-BI−/− (KO, white bar, n=14) mice were stained (anti-GPIIbIIIa antibody), and counted by flow cytometry. Results are averages from three experiments, each containing a minimum of 3 mice/group; ** P<0.001 B. WT (black diamonds) and SR-BI KO (KO, white squares) mice were intravenously infused with biotin to label platelets in vivo. Mice were then bled each day for five days and the fractions of platelets labeled with biotin were determined by flow cytometry. The percentage of biotinylated platelets was defined as 100% on day 0. (determined 30 minutes after infusion of biotin-NHS) (n=4–5, *P<0.05, **P<0.001).