Abstract: A new, non-toxic pharmaceutical composition for the treatment and prevention of invasive pulmonary aspergillosis has been discovered. The new pharmaceutical composition includes a physiologically compatible carrier and an agent which inhibits the proteolytic activity of the extracellular elastolytic serine protease produced by aspergillus. The agent preferably comprises a serine protease inhibitor, more preferably a subtilisn-type inhibitor, most preferably streptomyces subtilisin inhibitor. Such pharmaceutical compositions are effective at reducing the incidence of mortality due to invasive pulmonary aspergillosis and are also effective at reducing the invasion of lung tissue and the tissues surrounding the lungs by the germinating hyphae of Aspergillus.