We report the course of a patient with severe autoimmune neutropenia in whom only transient responses occurred with corticosteroids, antilymphocyte globulin and granulocyte-colony stimulating factor, and who was resistant to treatment with azathioprine, cyclosporin and intravenous immunoglobulin. A 10 d course of intravenous Campath-1H monoclonal resulted in a sustained haematological response. The long-lasting effect of Campath-1H may be due to its remarkable ability to induce a profound and prolonged peripheral blood T lymphopenia.