 The standard as well as the subjects whole-blood samples will be corrected for elution and also for the residual activity in the cellular fraction one day after the infusion. Data points 24 hours post-infusion will be used to calculate in vivo recovery after all radioactive corrections have been made. The radioactivity of the samples will be determined by use of a gamma counter. A multiple-hit model will be used to estimate the survival of the radioactively labeled platelets. 