The kallikrein-kinin system was studied in middle ear effusions from 28 ears suffering from otitis media with either a purulent, mucopurulent, serous or seromucinous, or mucoid effusion. Kinin, kininogen, kininase, kallikrein, prekallikrein, and protein were measured in these secretions. The findings suggest that the concentration of kinin is greatest in the serous and seromucinous effusions and lowest in the mucoid effusion. This is also true for kininogen and total protein. These studies suggest that the vasoactive polypeptide system is present in most middle ear effusions and that the concentration of the components of this system are different for different effusions.