Aggregation is normal in platelets from cellubrevin/VAMP-3 knockout mice. PRP was prepared from wild-type (+/+), heterozygous (+/–), and cellubrevin/VAMP-3 knockout mice (–/–) and diluted to a final concentration of 0.09% sodium citrate as described in “Materials and methods.” PRP was preincubated with 1 mM CaCl₂ at 37°C for 5 minutes prior to incubation with agonist as indicated.