Inclusion Criteria:

- Cytologically/histologically confirmed primary myelodysplastic syndrome (pMDS) with a
favorable risk profile, i.e., low or intermediate I risk group according to IPSS
(<10% blasts, no unfavorable karyotype)

- platelet count ≥50.000/µl

- absolute neutrophil count ≥1.000/µl

- age ≥18 years at the time of signing the informed consent form

- Karnofsky performance status > 50%

- written informed consent to participate

- erythropoietin level > 200 mU/ml or failure of previous therapy with erythropoietin

- patients in whom allogeneic bone marrow transplantation, treatment with growth
factors or immune therapy is not possible due to medical or biologic reasons or
patients in whom such a therapy would be possible but who do not agree to such a
therapy for personal reasons

- females of childbearing potential (FCBP, see page 23) must agree to one reliable form
of contraception or to practice complete abstinence from heterosexual intercourse
during the following time periods related to this study: 1) for at least 4 weeks
before starting study drug; 2) while participating in the study, even during
treatment interruptions; and 3) for at least 4 weeks after discontinuation from the
study.

Exclusion Criteria:

- patients with 5q deletion

- MDS treated with experimental therapy or chemotherapy within 4 weeks prior to start
of treatment with study drugs

- previous treatment of MDS with valproic acid or lenalidomide as monotherapy patients
suitable for chemotherapy, therapy with growth factors or allogeneic bone marrow
transplantation and who are willing to start such a therapy

- hypersensitivity to thalidomide

- insufficient liver function (bilirubin, AST or ALT > 2 x ULN)

- hepatic disease [details see full protocol]

- markedly impaired renal function (serum creatinine > 2mg/dl)

- pregnancy, breast feeding, lactation, refusal to use safe contraceptive methods
during the study

- psychiatric disease or addiction with impaired ability to act and make decisions
according to one's free will

- participation in another interventional study 4 weeks prior to or during this study

- known hypersensitivity or allergies to one of the study drugs or their ingredients

- plasmatic coagulation disorder