Human placentae have been extracted with combinations of enzymes to optimize the release of mononuclear phagocytes. A mixture of trypsin-DNAase used in sequential extraction was found to provide the best yield of adherent cells which were stable in culture. The majority of adherent cells exhibited phagocytic function and expression of receptor for IgG-Fc (FcR). Subsequent studies established that these functions were co-expressed by the same cells. The FcR+ cells were also shown by immunofluorescence with monoclonal antibodies to display monocyte-macrophage distinctive antigens and class I and class II MHC antigens. The placenta has thus been shown to provide a rich source of class II-positive macrophages suitable for immunological studies.