For quantification of the number of molecules of IgG anti-D bound to RBC, a combination of flow cytometry plus Sol-ELISA was found more accurate than Sol-ELISA alone. However, some Rh MAbs gave very low values of cell-bound IgG using flow cytometry. Monocyte-mediated haemolysis correlated well with the number of molecules of red cell-bound IgG1 anti-D. The monocyte phagocytosis assay was found more sensitive but less quantitative than the monocyte ADCC assay. Most monoclonal antibodies mediated little haemolysis by lymphocytes in ADCC assays, and haemolysis was not related to IgG concentration, titres or cell-bound IgG.