Patients in both groups will be assessed in clinic two weeks after starting treatment, and then monthly to see if they are having any side effects to hydroxyurea. We will also check to see if the MTD has been reached. Once it is decided that the patient has reached their maximum dose, they will continue to be monitored for two additional clinic visits (approximately eight additional weeks) to complete collection of end-of-study biological blood and urine samples and to ensure that there is no late harmful effects from hydroxyurea. The maximum time the patient will be on the study is 12 months after starting hydroxyurea therapy.