Sixty-four PCR-markers previously assigned to the short arm of chromosome 17 and two newly established STSs were localized on a hybrid cell-YAC clone panel. The 66 STSs fell into 23 unique retention patterns, providing a map converting the entire short arm of human chromosome 17 with an average resolution of approximately 1.2 Mb. The combination of radiation-reduced hybrids, somatic cell hybrids and selected YAC clones enabled the precise localization of break-points in two cell hybrids. Since polymorphic STSs from the CEPH as well as the UTAH genetic map were used in this study, a physical link has been generated between these two high resolution genetic maps. FMR1L2, a second FMR1 autosomal homologue has been identified and assigned to a genomic interval between D17S796 and D17S799.