Approximately 70% to 80% of Rh-positive adults and children with acute or chronic immune thrombocytopenic purpura or HIV-related thrombocytopenia respond to infusions of anti-D immunoglobulin. The speed of onset of response is slower than that seen with intravenous immunoglobulin. Anti-D immunoglobulin is well tolerated, with occasional adverse reactions similar to those seen in treatment with polyclonal intravenous immunoglobulin, but anemia requiring blood transfusion can occur. Response is generally better in younger patients and those who have responded to other forms of treatment. Inhibition of Fc receptor-mediated platelet destruction by anti-D immunoglobulin-opsonized erythrocytes is the most likely mechanism of action, although the relative ineffectiveness of a monoclonal anti-D immunoglobulin preparation in treatment of immune thrombocytopenic purpura suggests that other mechanisms may exist. Hepatitis C has been transmitted by intravenous anti-D immunoglobulin preparations when used in the prevention of Rh immunization, prior to the introduction of screening donor plasma for hepatitis C virus antibodies. However, an intravenous solvent-detergent-treated preparation is now available.