- This proposal is for a randomized, placebo-controlled pilot clinical trial designed to obtain data on the effects of EPO in humans with persistent post-concussive symptoms after TBI. The primary objective is to evaluate effect of 4 week administration of recombinant erythropoietin on numbers of circulating endothelial progenitor cells in patients with persistent symptoms during the subacute period after TBI. This information will guide the design of a future definitive study.