To Demonstrate Superiority of Decitabine Over Azacitidine in Subjects With Intermediate- or High-risk MDS.

Inclusion Criteria Subjects who meet all of the following criteria may be included in the study: 1. Must have a diagnosis of primary myelodysplastic syndromes (MDS) of Intermediate-1 transfusion dependent, Intermediate-2, or High-risk \[defined by International Prognostic Scoring System (IPSS) score of ≥0.5\] and recognized French-American-British (FAB) classifications 2. Male or female, 18 years of age or older with signed informed consent 3. Adequate renal function 4. Demonstrated normal liver function 5. Female subjects of childbearing age must have negative pregnancy test within 1 week of study entry and agree to use adequate contraception for the duration of the trial and for a minimum of six months after last dose of decitabine or azacitidine received. 6. Male subjects must agree to use adequate contraception for the duration of the trial and for a minimum of six months after last dose of decitabine or azacitidine received. Exclusion Criteria Subjects who meet any of the following criteria will be excluded from participation in the study: 1. Current use of radiotherapy for extramedullary disease for 2 weeks prior to entering study (permitted if \> 2 weeks from study entry and if recovered from toxic effects of therapy) 2. Systemic fungal, bacterial, or viral infection which is not controlled (i.e., ongoing signs or symptoms of infection and without improvement despite appropriate treatment) 3. Pregnancy or current lactation 4. Significant concurrent disease, illness, or psychiatric disorder 5. Treatment with an investigational agent 30 days prior to the first dose of decitabine or azacitidine