The clinical activity of rituximab, a chimeric monoclonal antibody which binds to the CD20 antigen, was evaluated as a single first-line therapy for patients with follicular non-Hodgkin lymphoma (NHL). Fifty patients with follicular CD20⁺ NHL and a low tumor burden were analyzed for clinical and molecular responses. They received 4 weekly infusions of rituximab at a dose of 375 mg/m². The response rate a month after treatment (day 50) was 36 of 49 (73%), with 10 patients in complete remission, 3 patients in complete remission/unconfirmed, and 23 patients in partial remission. Ten patients had stable disease, and the disease progressed in 3 patients. One of 13 (8%) patients in complete remission, 9 of 23 (39%) patients in partial remission, and 5 of 10 (50%) patients with stable disease exhibited disease progression during the first year. Within the study population, 32 patients were initially informative for polymerase chain reaction (PCR) data on bcl-2–J_Hrearrangement. On day 50, 17 of 30 patients (57%) were negative for bcl-2–J_H rearrangement in peripheral blood, and 9 of 29 (31%) were negative in bone marrow; a significant association was observed between molecular and clinical responses (P < .0001). At month 12, 16 of 26 patients (62%) were PCR negative in peripheral blood. These results indicate that early molecular responses can be sustained for up to 12 months and that this response is highly correlated with progression-free survival. Rituximab has a high clinical activity and a low toxicity and induces a high complete molecular response rate in patients with follicular lymphoma and a low tumor burden.