The majority of peripheral blood monocytes strongly positive for the lipopolysaccharides (LPS)-receptor CD14 are negative for Fcgamma receptor type III (CD16). However, a subset of monocytes coexpressing CD14 and CD16 accounts for about 8% of all monocytes. This population exhibits features of tissue macrophages, and is largely expanded (> 20%) during acute and chronic inflammatory diseases including cases with pararheumatic systemic vasculitis. In addition, compared to normal controls, soluble CD14 (sCD14) is elevated (> 3 microg/ml) in serum specimens of these patients. CD14+/CD16+ monocytes show a higher phagocytosis rate than CD14+/CD16 negative cells, and express higher levels of interleukin-1 and major histocompatibility complex, such as histocompatibility antigens HLA-DR, -DP and -DQ antigens. Glucocorticoids downregulate expression of CD14 and rapidly deplete CD14+/CD16+ monocytes from peripheral blood. Patients under chronic immunosuppressive therapy exhibit low CD14/+/CD16+ rates, which may rise during infectious and non-infectious inflammatory complications, however. Thus, serial analyses for sCD14 and the proinflammatory CD14+/CD16+ subset of monocytes suggest a valuable tool monitoring patients under immunosuppressive and/or antiinflammatory therapy.