Prenatal typing for RHD, or Kell are the most commonly demanded. But molecular typing may also be employed, to confirm the presence of a weak Fyb variant (FY*X), to define weak RHD antigens (Du), or to tell the original blood groups from a polytransfused patient. This shows, that molecular typing techniques offer an interesting addition to well established standard serology. Presently, with respect to blood groups, molecular biologists and medical doctors seem to be challenged by the identification of un- or weakly expressed alleles. Also, the "non-presence" of RHD - a hypothetical RHd allele - and its molecular background is of big interest with clinical implication.