The exact number of lysozyme- and alpha-1-antitrypsin-positive macrophages in the synovial membrane in rheumatoid arthritis and osteoarthrosis was investigated by the PAP-technique. There is a positive correlation between the number of macrophages in the intima, as well as in the adventitia of the synovial membrane, and the local immunological activity of rheumatoid arthritis. However, there exist significantly less positive macrophages in osteoarthrosis. The significant increase of macrophages in cases of rheumatoid arthritis is an expression of immunopathological mechanisms that have a pathogenetic importance for the induction and recidivity of arthritis. These facts justify therapy with antirheumatica to influence macrophages.