At present RHD incompatibility is still an obstetric problem despite prophylactic treatment. A very welcome recent technical advance has now made it possible to determine the foetal RHD status in a non-invasive risk-free manner using cell free foetal DNA in maternal plasma. In some cases, however, where there is a high risk that the foetus may be affected by HDN (haemolytic disease of the newborn), it may be of interest to determine whether the father is hetero- or homozygous for the RHD gene, since in the former instance there is only a 50% chance that the pregnancy is affected. It has recently been shown that quantitative PCR assays, in particular real-time Taqman PCR, can be used to determine the RHD gene dosage, and also to determine foetal aneuploidies. We demonstrate that the same real-time Taqman PCR assay we had previously developed for non-invasive analysis of the foetal RHD gene and the foetal Y chromosome from maternal plasma can be used to determine the paternal RHD genotype.