The standard as well as the subject's whole-blood samples will be corrected for elution and also for the residual activity in the cellular fraction on Day 8. The first four data points post-infusion will be used to calculate in vivo recoveries and survivals 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, with a computerized program "COST," will be used to estimate the recovery and survival of the radioactively labeled platelets.