Inclusion Criteria:

Screening phase:

- Age > 18 years

- Patients with CD34+ AML or MDS post-allogeneic HSCT

- Written patient consent after consultation

Treatment phase

- AML/MDS: donor chimerism < 80% in the CD34+ subpopulation following allogeneic HSCT
in patients with CD34+ AML or MDS, but with no haematological relapse (blasts < 5% in
bone marrow)

- Leukocytes > 3 Gpt/l and platelets > 75 Gpt/l (transfusion-independent)

Exclusion Criteria:

- Known intolerance to 5-azacitidine or mannitol

- Uncontrollable infectious disease

- Patients with active hepatitis B or C or HIV infection

- Severe hepatic function impairment (ASAT and ALAT may not be above three times the
normal value) or hepatic cirrhosis, or malignant hepatic tumour

- Renal function impairment (creatinine > twice the normal value, creatinine clearance
< 50 ml/min)

- Pregnancy or lactation

- Women of childbearing age, except for those who meet the following criteria:

- postmenopausal (12 months natural amenorrhoea)

- postoperative (6 weeks after bilateral ovarectomy with or without hysterectomy)

- regular and correct use of a contraceptive method with an error rate < 1% per year
(e.g. implants, depot injections, combined oral contraceptives, intrauterine device -
IUD, whereby hormonal coils with a Pearl Index of < 1% are safer than copper coils)

- sexual abstinence

- Partner vasectomy

- Men who do not use one of the following for contraception:

- sexual abstinence

- post vasectomy

- condoms

- Participation of the patient in a drug trial outside the indication of allogeneic
transplantation up to four weeks before study initiation

- Addictive or other illnesses that prevent the person concerned from comprehending the
nature and impact, as well as potentical consequences of the clinical trial

- Evidence that the patient may intentionally not comply with the protocol, e.g. lack
of cooperation With the exception of a known allergic reaction or intolerance to
5-azacitidine, these criteria do not apply to the screening phase.