Background. Quadruple immunosuppressive induction therapy has been shown to markedly reduce the incident of acute rejection episodes without increasing the incidence of infectious complications after liver transplantation. However, the use of polyclonal antibody preparations (e.g., antithymocyte globulin [ATG]) is associated with side effects such as fever and tachycardia. To evaluate the efficacy and the safety of monoclonal antibody directed against the interleukin-2 receptor (BT563) in comparison with ATG as part of a quadruple induction regimen, a prospective, randomized study was conducted. Methods. Eighty consecutive adult recipients of primary orthotopic liver transplants were randomized to receive either BT563 (10 mg/day; days 0-12; n β«Ψβ¬ 39) or ATG (5 mg/kg/day; days 0-6; n β«Ψβ¬ 41) in addition to the standard immunosuppressive protocol consisting of cyclosporine, and prednisolone, and azathioprine. Results. Patients treated with BT563 had a significantly lower incidence of steroid-sensitive rejection episodes (3 vs. 11; P F 0.0.25) and also significantly fewer drug related side effects (4 vs. 18, P F 0.038) when compared with patients treated with ATG. The incidence of infectious complications was not different between the two groups. Patient survival