The gene for the Wiskott-Aldrich syndrome, an X-linked immunodeficiency disease, has been mapped between the RFLP markers DXS7 and DXS14 on the short arm of the X-chromosome. Close linkage to these markers permits accurate carrier detection and prenatal diagnosis. In one family with WAS patients in two generations, RFLP analysis was applied to three women at risk. It could be determined with more than 98.5% accuracy that these women were not carriers.