Schmorl is generally credited with being the first to report finding fetal cells in maternal blood. In 1893 he identified trophoblasts in the pulmonary circulation of women who had died of eclampsia. Years later, in 1969, Walnowska identified Y chromosomes in lymphocytes isolated from the blood of pregnant women carrying male fetuses and this was repeated by Herzenberg in 1979 in white blood cells recognised as fetal by their surface HLA-A2 expression. Other sporadic reports followed but not until the 1990's did investigation into harvesting fetal cells from maternal blood begin in earnest. The aim of this article is to review the progress made in isolating and analysing these cells for the purposes of prenatal diagnosis.