The GZ100 series comprises a panel of monoclonal antibodies which seem to be specific for human trophoblast antigens (with the exception of GZ111, which reacts with a number of other tissues). The GZ antibodies show different reaction patterns with different trophoblast cell types. As a panel the GZ antibodies recognize all trophoblast populations (Table 2). Thus these antibodies provide a means to distinguish between trophoblast cells and maternal cells. GZ112 might be used to sort out HLA-class I positive trophoblast cells of the basal plate without blocking the HLA antigenic determinant, since GZ112 is not an anti HLA-class I antibody. At present the antigens detected by the GZ antibodies seem to be proteins, most of them with molecular weights between 50 kD and 80 kD. The function of these antigens is unclear and will be studied in future.