The present invention describes CD37 antibodies, especially A2 and B2, for the treatment of patients with CLL, especially of patients belonging to a “high risk” or “ultra-high risk” group of patients. Those patients are either patients who are refractory to fludarabine treatment or patients who carry a genetic marker which is indicative for poor prognosis or increased risk of treatment failure, e.g. patients with TP53 dysfunction or deletion of chromosome 17p13, or patients after failure to previous anti-CD20 treatment. The ability of A2 and B2 to deplete CLL cells is high both in patient samples derived from patients with normal risk and with increased risk (“high risk” patients) and clearly superior to that of rituximab and alemtuzumab.