The aim of this laboratory workshop was to evaluate the state of knowledge concerning the demonstration of membrane glycoprotein specific anti-platelet antibodies. The main interest lay in investigating whether specific antibody detection offers possibilities to distinguish the chronic from the acute form of ITP. In five laboratories four different methods were applied to demonstrate such antibodies. These methods are briefly described and compared. In all, except two, of the 45 ITP samples anti-platelet antibodies could be detected by at least one participating laboratory, in 85% of the samples antibodies were found by two or more laboratories. For seven out of eight control samples no positive results were reported. The comparison of glycoprotein specific anti-platelet antibodies shows partly considerable differences which may be due to the different methods as well as the different antibodies used (monoclonal antibody against membrane glycoprotein and antihuman globulin sera). This laboratory workshop leads to the conclusion that by exchange of reagents and patient samples the different methods may be compared and evaluated. The results obtained allowed no further characterization of ITP. All participants agreed on the usefulness of further similar laboratory workshops.