Arthritic and histologically normal joints from swine in which arthritis had been produced by the intravenous inoculation of Erysipelothrix rhusiopathiae were used as a source of fluids for lysosomal enzyme determinations. Mean lysozyme activities in synovias from arthritic and histologically normal joints were 16.60 and 5.79 mug/ml, respectively. Acid phosphatase (ACP) was increased more than 8 times the activity in histologically normal joints, but there was no relationship between lysozyme and ACP, indicating the probability that 1 of these enzymes came from another source. The cytoplasmic enzyme, lactic dehydrogenase (LDH), was increased in proportion to ACP, indicating that cell death and not selective extrusion of lysosomal enzymes during phagocytosis was an important mechanism of enzyme release in arthritic joints. Lysozyme activities in synovias from histologically normal joints were often increased above companion serum concentrations, indicating the enzyme has a special role in the joint. Also, the ratio of activities of lysozyme to ACP in pig buffy coat lysates was different from the ratio of the 2 enzymes in synovias from arthritic joints.