Immunologic rejection is the major hazard to the short-term success of renal transplantation. Rejection may be (1) hyperacute (immediate graft dysfunction due to presensitization) or (2) acute (sudden change in renal function occurring within weeks to months). Rejection is usually detected by a rise in serum creatinine but may also lead to hypertension, fever, reduced urine output, and occasionally graft tenderness. A percutaneous renal transplant biopsy confirms the diagnosis. Treatment usually consists of a “pulse” of methylprednisolone. In refractory or particularly severe cases, 7-10 days of a monoclonal antibody directed at human T lymphocytes may be given. Antibody-mediated rejection may require the use of anti-B cell agents and/or plasmapheresis.