A large Danish pedigree segregating for X-linked retinitis pigmentosa (RPX) (Warburg and Simonsen 1968) was restudied for linkage analysis.Using two markers, i.e. the DNA base sequence polymorphism presented by the probe L1.28 defining the chromosomal segment DXS7, and the C-banding heteromorphism (Xcen) (Friedrich 1982), we were able to localize the RPX gene in Xp close to the centromere rather precisely.