Elastase, an enzyme in the azurophilic granules of polymorphonuclear cells (PMN), is like other granular PMN proteases characterized by its degradative activity at physiological pH towards native macromolecules as shown in a serum free medium. Joint tissue specimen obtained during elective surgery in cases of various rheumatic conditions were examined in order to elucidate the role of this enzyme during joint cartilage destruction. An indirect immunofluorescence microscopic technique utilizing a rabbit immunoglobulin G preparation raised against purified elastase was used for this purpose. Immunoreactive elastase was seen bound to cells which were recognized as PMN by their nuclear characteristics and staining in a histochemical reaction with naphtol AS-D chloroacetate. PMN were encountered more or less often in the pannus but clearly accumulated in a significant amount at the pannus-cartilage junction in one case of rheumatic monarthritis and three out of four cases with rheumatoid arthritis. This finding shows that PMN--contrary to other descriptions--belong to the morphologic characteristics of inflammatory rheumatic conditions and directly supports the hypothesis that PMN enzymes play an active role in rheumatoid cartilage destruction.