During chronic otitis media intact immunoglobulins are split by extracellular bacterial proteinases into fragments of different molecular weight, The most malignant extracellular proteinases with the greatest proteolytic activity against intact immunoglobulins are the bacterial proteinases of Pseudomonas aeruginosa. These proteinases cannot be inhibited by the other serum proteinase-inhibitor except for Alpha-2-Macroglobulin of the human blood serum. This inhibitor has a very high molecular weight, so that we cannot find it in a higher concentration in the middle-ear-secretory. We can liberate this inhibitor by injuring the blood vessels during a tympanoplasty. In this way we get an inhibitory effect against these proteinases and combined with an appropriate antibiotic therapy we can cure a chronic otitis MEDIA. In order to demonstrate that there are immunological reactions in the middle ear against homografted ossicles, various transplantation with homologous ossicles have been performed between two inbreeding rat strains. After sensitisation of the host animals against antigens of the donor animals with skin grafts a reliable histologic infiltration with plasma cells and lymphocytes and the rejection of the graft could be insured. After a simple homologous transplantation without sensitisation, these rejection reactions occurr only rarely and in a diminished form. Cialit storage of middle ear ossicles decreases the solubility of the contained proteins and this in turn diminishes the antigenicity, the amount the antigens, or it retards their liberation. It is for these reasons that Cialit-stored ossicles are more slowly transformed, and there are less inflammatory reactions and adhesions than with untreated ones. The osteogenetic capability of the ossicles is not affected by the Cialit storage.