Extracts of Dermatophagoides pteronyssinus and D. farinae were shown to contain a variety of 30 kDA serine proteases, including trypsin, chymotrypsin, and an elastase-like enzyme. The mite trypsin, unlike chymotrypsin and the elastase enzyme, was heterogeneous with regard to charge. The enzymes were shown to be present at higher concentration in fecally enriched extracts than in whole mite extracts. The proteases were shown to induce vascular permeability and to detach cells in tissue culture. Further study showed that the mite elastase induced non-IgE mediated rat mast cell degranulation. Such properties may contribute to immunogenicity. (C) 1994 Wiley-Liss, Inc.