The presence of auto-antibodies against the formed elements of the blood in part of the patients suffering from haemolytic anaemia, thrombopenia and leucopenia has fully been established. The question arises whether auto-antibodies against tissues may be demonstrated in diseases where the etiology and pathogenesis are still unknown and an immunological cause is suspected. The comparable circumstances preceding the appearance of thrombocytopenic and vascular purpura was emphasized by Dameshek . Both have in common the more or less acute appearance of the symptoms, sometimes after infection (“grippe”, sore throat etc.) or after the use of drugs. In part of the cases with thrombopenia autoantibodies against thrombocytes can be demonstrated. By injecting animals with heterologous anti-vessel endothelium serum it proved to be possible to provoke a syndrome that shows much resemblance with the Schönlein Henoch purpura in human beings [4,9]. With regard to the experiments of Bedson [1, 2], later confirmed by Elliot and Whipple , the question arises whether an immunologic vascular component might be involved in thrombocytopenic purpura. Stefanini  found precipitating antibodies in 6 out of 8 cases of Schönlein Henoch purpura and in 3 out of 4 cases of polyarteritis nodosa, using vessel extracts from aortae of newborns and intima tissue from aortae of adults. In view of the importance of such findings, an attempt was made to reproduce the results of Stefanini.