Current knowledge of the pathophysiology of bacterial infections is elementary. The initial events leading to the invasion of host tissues are a matter of conjecture for many bacterial organisms. This is particularly true for pneumococci, the most frequent causative organisms of acute otitis media. Bacterial enzymes may account for the initial disruption of host tissues, and this study explored their role in the infectious process. As a first step, pneumococcal cultures were analyzed, and significant levels of the enzymes lipase and hyaluronidase were demonstrated. Secondly, the presence of these enzymes in middle ear effusions were explored in an animal model of acute otitis media. The enzymes reached peak levels at seven days. The third and most important portion of the study examined the significance of these enzymes in producing inflammation and alterations in the middle ear cavity of normal experimental animals. This portion was a histologic comparison of temporal bone specimens and demonstrated that marked acute and chronic changes can be induced by placing solutions of these enzymes in the middle ear cavity. This study concludes that bacterial enzymes play an important role in the induction of acute otitis media.