The efficacy and safety of zanolimumab (HuMax-CD4) in patients with relapsed or refractory peripheral T Cell lymphoma (PTCL) was evaluated. Twenty-one adult patients with relapsed or refractory CD4(+) PTCL of non-cutaneous type (angioimmunoblastic T cell lymphoma (AITL) n = 9, PTCL-not otherwise specified (NOS) n = 7, anaplastic large cell lymphoma (ALCL) n = 4 and enteropathy type T cell lymphoma n = 1) were treated in a single-arm multi-centre study, with weekly intravenous infusions of zanolimumab 980 mg for 12 weeks. Median age was 69 years (range 26-85). Seventeen of the patients had advanced stage disease (Ann Arbor stages III-IV). Objective tumour responses were obtained in 24% of the patients with two complete responses unconfirmed (CRu) and three partial responses (PR). One of the CRus lasted more than 252 d. Responses were obtained in different PTCL entities: AITL (n = 3), ALCL (n = 1) and PTCL-NOS (n = 1). In general, the trial drug was well tolerated with no major toxicity. Zanolimumab at a dose of 980 mg weekly demonstrated clinical activity and an acceptable safety profile in this poor-prognosis patient population, suggesting that the potential benefit combining zanolimumab with standard chemotherapy in the treatment of PTCL should be investigated.