Analyses of 20 middle ear effusions and plasma from 15 patients with serous otitis media demonstrated a marked local release of the granulocyte proteases, elastase, and collagenolytic neutral protease in the effusions. Furthermore, activation of C3 and complexes with antiplasmin were demonstrated. Complex formations between the granulocyte proteases and the protease inhibitors, α1-antitrypsin, α2-macroglobulin, and antileukoprotease were shown. A residual inhibitory capacity for α1-antitrypsin and antileukoprotease was also demonstrated in the middle ear effusions.