The purpose of this study is to compare the safety of SANGUINATE™ versus Hydroxyurea in patients suffering from Sickle Cell Disease.

Inclusion Criteria:

• Patients with Homozygous (HbSS) Sickle Cell Anemia;
• Hb levels: >6g/dL - <10g/dL;
• Age : >18 years old;
• Frequency of ER hospitalizations < 6x/yr for SCD pain events documented "medical history".

Exclusion Criteria:

• Patients, who are on chronic transfusion program, defined as regular transfusions every 2-8 weeks;
• Allergic to Hydroxyurea;
• History of clinical significant disease, as determined by the Investigator;
• History of allergy or major allergic reaction considered to be clinically significant by the Investigator;
• Screening assessments considered to be abnormal by the Investigator;
• Patient has sever pulmonary hypertension (index >3 meters per sec);
• Donated blood within 60 days of screening or otherwise experienced blood loss of >250 mL within the same period;
• Intending to begin new concomitant drug therapy or over-the-counter medication anytime from scree4nin to the time of administration of study drug;