Effect of Recombinant Erythropoietin on Numbers of Circulating Endothelial Progenitor Cells in People With Persistent Symptoms During the Subacute Period After Traumatic Brain Injury

Background: \- Traumatic brain injury (TBI) injures blood vessels in the brain. Endothelial progenitor cells (EPCs) help the body form new blood vessels. The drug erythropoietin (EPO) helps the body make more blood cells and might help make blood vessels. Researchers want to see if EPO helps people with TBI. Objective: \- To see whether erythropoietin increases the number of endothelial progenitor cells circulating in the blood and changes reactivity of brain vessels. Eligibility: \- Adults age 18 70 who had a TBI 3 7 days ago and still have symptoms. Design: * Participants will be screened with medical history and blood tests. Vital signs will be taken. * Visit 1: * Medical history, physical exam, and blood sample. * Neuropsychological tests of memory, attention, and thinking. These include written and spoken questions, tests on paper or computer, and simple actions. * Magnetic resonance imaging (MRI) scan with carbon dioxide. Participants will lie on a table that slides in and out of a metal cylinder. For part of the scan, participants will wear a breathing mask like a snorkel and wear a nose clip. * Study drug or placebo injection under the skin of the arm, leg, or buttock. * Visits 2, 3, and 4 will be 1 week apart. * Blood sample. * Review of TBI symptoms and any drug side effects. * Study drug or placebo injection under the skin. * Visit 5 will be 1 week after visit 4. Visit 6 will be 6 months after participants start the study. * Blood sample. * Review of TBI symptoms and any drug side effects. * Neuropsychological tests. * MRI with carbon dioxide.