The rate of thrombin-induced secretion of granule cargo is normal in cellubrevin/VAMP-3 platelets. Platelets from null (–/–; filled symbols) and wild-type (+/+; open symbols) mice were prepared as described in “Materials and methods.” Aliquots of intact washed platelets (2.5 × 10⁸ cells) were incubated with 0.7 mM CaCl₂ at room temperature for 5 minutes and then incubated with thrombin (0.5 U/mL) at room temperature for the indicated times. Release of [³H]-5HT from dense core granules (○,•), of PF4 from alpha granule release (▵,▴), and of hexosaminidase from lysosomes (▪,□) were measured as described in “Materials and methods.” Release is calculated as the percent of total platelet marker present in reaction supernatant. The points represent the average of triplicate measurements, and the standard deviation is indicated.