For prenatal cytogenetic analysis, cells are now sampled from the amniotic sac, a procedure which carries some risk and some women will not submit to it. There is a desire to find a less invasive and less risky sampling procedure. A number of laboratories are developing procedures to enrich fetal trophoblasts from maternal blood. These procedures are not expected to provide pure populations of fetal cells, so a means of verifying fetal origin for female fetuses is needed. To verify fetal origin, we propose to develop a statistics-based image analysis of metaphase chromosomes labelled with fluorescent alpha satellite DNA probes. We base our strategy on the fact that the number of copies of alpha-satellite DNA repeats is variable in human populations, so an analysis of intensity of the fluorescent "light stars" emanating from each chromosome should allow us to distinguish fetal from maternal cells. This procedure uses the same metaphase spreads prepared for standard prenatal cytogenetics, so standard analysis can be carried out on previously stored images of the fetal-verified cells. A simpler version of these procedures will provide a means for uniquely identifying humans for paternity and forensic purposes.