Extracorporeal procedures such as plasmapheresis or protein a apheresis have been applied successfully to remove autoantibodies in the treatment of severe forms of various autoimmune diseases. A newly developed immunoapheresis technique that uses columns containing polyclonal anti human immunoglobulin (Ig) antibodies was investigated in four patients with idiopathic thrombocytopenic purpura (ITP). A series of two to four treatments were performed, and the period between the two series was dependent on the actual thrombocyte count. A total of 38 treatments was carried out. During the first apheresis, IgG declined to a mean of 52.7% of the initial concentration. The IgG subclasses one through four were decreased to the same extent. The IgA was lowered to 64.4%, and IgM was lowered to 66.7%. A series of four aphereses yielded a 75-80% decline of the different Ig species. A further decrease in Ig would have been possible, but was not aimed at in this study. All Ig fractions reincreased between the two series. In two patients, a rise in thrombocytes as a response to treatment was observed. Apart from three hypotensive reactions and one episode of hypocalcemia, no further side effects occurred in 38 treatments. The authors conclude that Ig apheresis with anti human Ig antibodies is an effective and safe form of treatment. Its effect on the clinical course of autoimmune diseases merits further investigation.