With the introduction of human monoclonal antibodies against antigens of the Rh-system it was possible to solve a series of problems, as, for instance, the permanent availability of reagents. Another problem, the classification of D-categories with a panel of specific monoclonal antibodies, also might be solved by the production of such antibodies. Especially the classification of Cat. VI-cells is of great importance. We present a panel of five human monoclonal antibodies useful for the definition of Rh-D categories. The antibodies are designated as BS221, BS227, BS228, BS230 and BS231. By positive or negative reactions with expected category cells it is possible to determine the corresponding category. All Cat. VI-cells of a defined panel could be identified. Of particular interest is the antibody BS221 due to its reactivity with Cat. VI-cells. The fact, however, that BS221 is missing the detection of some Cat. VI-cells indicates a further subdivision of Cat. VI.