Angioimmunoblastic T cell lymphoma is a distinct entity for which there is no standard therapy. On the basis of the rationale that CsA may represent a novel drug for AITL, a disease with considerable immune dysregulation, and encouraging case reports, the authors have treated 12 patients with this agent. Ten had failed prior steroids and/or chemotherapy and two had no prior therapy. CsA was administered at a dose of 3 - 5 mg/kg PO bid for 6 - 8 weeks and gradually tapered by 50 mg every 1 - 3 weeks. Responding patients received a maintenance dose of 50 - 100 mg, with a gradual taper after a maximal response was achieved as tolerated. Doses were titrated for renal dysfunction or hypertension. CsA levels were not monitored. Eight of 12 patients responded (three complete and five partial remissions). Dose reductions were required in six patients; renal insufficiency (n = 3), fatigue (n = 2), and hypertension (n = 1). Two patients developed acute infections and one patient died shortly after active treatment. These results suggest that CsA deserves further testing as a novel therapy for AITL. By interrupting T-cell activation, CsA may alter the immune dysregulation that characterizes AILT. The efficacy of CsA is being explored in patients with recurrent AILT in a prospective trial (ECOG 2402).