The combination of Fludarabine and Cyclophosphamide have yielded overall response rates of over 80% in previously untreated patients with indolent Non-Hodgkin-Lymphoma. However, hematotoxicity rates were high with Grade 3 and 4 toxicities of over 50%. Several studies have indicated that the treatment with Pentostatin and Cyclophosphamide causes lower hematotoxicity rates than the combination of Fludarabine and Cyclophosphamide. To evaluate the efficacy and safety of treatment with Pentostatin/Cyclophosphamide immuno-chemotherapy for patients with newly diagnosed or relapsed Immunocytoma/Morbus Waldenström, B-cell chronic lymphocytic leukemia (B-CLL) and other indolent CD20-positive B-NHL, an open, non-randomized, multi-center prospective phase II-study to evaluate the efficacy and safety of treatment with immuno-chemotherapy is conducted. Treatment consists of 6 courses of Pentostatin (4mg/m² on day 1), Cyclophosphamide (600mg/m² on day 1) and Rituximab (375mg/m² on day 0) administered every three weeks. Patients achieving complete or partial remission undergo maintenance therapy consisting of 8 courses of Rituximab (375mg/m²) administered every three months over a period of 2 years.