Inclusion Criteria:

1. Patients with first or later relapse of histologically (WHO classification) confirmed:

   • follicular lymphoma
   • marginal zone lymphoma
   • lymphoplasmocytic lymphoma
   • mantle cell lymphoma requiring therapy and not eligible for curative treatment
2. Measurable disease (at least one lesion >= 1.5 cm) documented by CT scan
3. Age >= 18 years
4. ECOG performance status <=2
5. Life expectancy of at least 6 months
6. Ability to understand the patient information and informed consent form
7. Signed and dated written informed consent is available

Exclusion Criteria:

1. Any other NHL not listed in inclusion criterion 1
2. Peripheral lymphocyte count > 20 x 10x9/l
3. Known or suspected central nervous system (CNS) involvement by NHL
4. a)Clinical history of CNS pathology (except headache/migraine) b)Evidence for presence of inflammatory lesions and/or vasculitis on MRI
5. Autologous stem cell transplantation within 26 weeks prior to study entry
6. Allogeneic stem cell transplantation
7. Cancer chemotherapy within 6 weeks prior to study entry
8. Radiotherapy within six weeks prior to study entry
9. Treatment with rituximab within 12 weeks prior to study entry
10. Prior treatment with alemtuzumab
11. Treatment with any investigational agent within 12 weeks prior to study entry
12. Contraindication for any of the concomitant medications

13. Abnormal renal or hepatic function as defined below:

    • AST (SGOT) and/or ALT (SGPT) >= 2 x upper limit of normal (ULN)
    • total bilirubin >= 1.5 x ULN
    • serum creatinine >= 2 x ULN

14. Indication of hypercoagulative state as defined below:

    • D-dimer >=2.5 x ULN
    • antithrombin activity <LLN
15. Presence of human anti-murine antibodies (HAMA) or known hypersensitivity to immunoglobulins
16. History of malignancy other than B-cell lymphoma within 5 years prior to study entry, with the exception of basal cell carcinoma of the skin or carcinoma in situ of the cervix
17. Active infection or known bacteriemia
18. Any concurrent disease or medical condition that is deemed to interfere with the conduct of the study as judged by the investigator
19. Regular dose of corticosteroids during the four weeks prior to D1 of this study or anticipated need of corticosteroids exceeding prednisone 20 mg/day or equivalent, or any other immunosuppressive therapy within 12 weeks prior to study entry
20. Known infection with human immunodeficiency virus (HIV) or chronic infection with hepatitis B or hepatitis C virus
21. Pregnant or nursing women, or women of childbearing potential not willing to use an effective form of contraception during participation in the study and at least three months thereafter. Male patients not willing to ensure that during the study and at least three months thereafter no fathering takes place.