Elastolytic activity by live human monocytes (M phi) is mainly caused by cell surface related leucocyte elastase, capable of degrading matrix components. In order to examine the possible correlation between enzyme activity and tissue turnover in the joint, we examined 24 synovial fluids for M phi elastolytic activity, using the levels of synovial fluid interleukin-6 and serum C reactive protein as additional markers of cell activation. Proteoglycan levels were measured as an indication of cartilage degradation and the types I and III procollagen propeptides as markers of synovial membrane turnover. We found that elastolysis by live M phi and the levels of interleukin-6 and C reactive protein correlated significantly with proteoglycan concentrations but not with the procollagen propeptides. These findings suggest that human M phi elastolytic activation is a biologically relevant factor in cartilage degradation, but is unrelated to the collagen metabolism of the synovial membrane.