Abstract.A new class of immunogenetic models is presented, which is based on the assumption of complex (cross‐reacting) antibodies and complex antigens (i.e. antigens with more than one kind of antigenic determinants).The model is applied to the Rh‐system at the 9 reagent‐8 haplotype level and shown to give a simplified conceptual image of the Rh‐system at this level. It is demonstrated that the same model could also have been deduced from a conventional (simple‐complex) model if only the discovery of the 9 base reagents had occurred in a different historical sequence.Several experimental data which are difficult to accomodate in a conventional model appear strongly to support the new model, which also is in better harmony with theconceptual(but not notational) image of antibody‐antigen relations expressed by many workers in the field.The new model only requires 5–6 symbols to account for those basic Rh‐data which in a conventional simple‐complex model would require 9–10 symbols. It is obvious that this new class of serologic models is also of great interest in other fields