Efficacy and Safety Study of SH T 586 in Combination With Rituximab to Treat Low-Grade NHL

Inclusion Criteria: * Patients with CD 20 positive, relapsed/refractory indolent lymphoma. (Regimens of prior chemotherapy are limited to 2; prior rituximab treatments up to 16 times are allowed.) * Patients with measurable lesions (\> 1.5 cm). * Patients who have not received any treatment for more than 4 weeks after completing previous therapies (6 months in the case of antibody therapies). * ECOG performance status: 0 - 1 * Patients with adequately maintained organ functions. Exclusion Criteria: * Patients with infectious disease, serious complications, serious gastrointestinal symptoms, serious bleeding tendency, serious CNS symptoms, fever \</=38 °C, interstitial pneumonia or pulmonary fibrosis, active other malignancies, autoimmune hemolytic anemia or the history of the disease, or glaucoma. * Patients who are positive for HBs antigen, HCV antibody, or HIV antibody. * Patients who received G-CSF or transfusion within 1 week before the registration. * Patients with the history of allergies to purine nucleoside analogue. * Patients who experienced serious hypersensitivity or anaphylaxis to rituximab or mouse protein-derived products. * Patients who had ever received prior therapy with fludarabine phosphate injection, pentostatin, cladribine, SH T 586, blood stem cell transplant, or monoclonal antibody therapy other than rituximab to NHL (including radioimmunotherapy). * Patients who had progressive disease within 6 months of receiving therapy including rituximab. * Women who are pregnant, of childbearing potential, or lactating. * Patients who do not agree to practice contraception.