The understanding of the separate molar syndromes has been much advanced by the application of genetic techniques of chromosome banding. These techniques allow not only for the identification of each chromosome but also for the discrimination between the two homologues (one paternal and one maternal) of chromosomes 1,3,4,9,13–16,21,22;1–6 in addition, the parental origin of the chromosomes of complete and partial hydatidiform moles could be determined. Analysis of polymorphic enzyme loci,3,6 human lymphocyte antigens (HLA) specificities.7 and, more recently, restriction fragment length polymorphisms in DNA using cloned DNA probes have also been utilized to this end.8,9