A method of controlling the amount of a biologically active substance binding to a cell surface having both receptors to the substance and receptors for the Fc domain of an antibody that can complex with the substance or other antibodies that can complex with the substance. By exploiting the generally more numerous Fc receptor sites, substance binding can be increased and/or controlled. Method contemplates controlling amounts of substances such as cytokines, hormones, and growth factors that are associated with cells such as monocytes, macrophages, granulocytes, B cells, T cells, and platelets. Method is illustrated using conjugated antibodies to tissue necrosis factor (TNF) to increase the binding of TNF to monocytes.