Ofatumumab is a fully human anti-CD20 monoclonal antibody that induces antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity in CD20-expressing B lymphocytes. Ofatumumab is highly potent in lysing B cells, and this appears to stem from its binding site on the short extracellular loop of the target CD20 protein and its slow release from the target molecule. In a pivotal, noncomparative study in patients with fludarabine- and alemtuzumab-refractory chronic lymphocytic leukaemia (CLL), ofatumumab induced objective responses in 58% (99% CI 40, 74) of patients, which met a prespecified superiority criterion. The median duration of response was 7.1 months. The median progression-free survival was 5.7 months and the median overall survival was 13.7 months. In patients with fludarabine- and alemtuzumab-refractory CLL, infections and neutropenia were the most frequent treatment-related adverse events (all grades) that occurred during ofatumumab treatment; infections that commenced during treatment led to death in five patients (8%).