A familial early-onset breast cancer gene (BRCA1) has been localized to chromosome 17q21. To characterize this region and to aid in the identification of the BRCA1 gene, a physical map of a region of 1.0-1.5 Mb between the EDH17B1 and the PPY loci on chromosome 17q21 was generated. The physical map is composed of a yeast artificial chromosome (YAC) and P1 phage contig with one gap. The majority of the interval has also been converted to a cosmid contig. Twenty-three PCR-based sequence-tagged sites (STSs) were mapped to these contigs, thereby confirming the order and overlap of individual clones. This complex physical map of the BRCA1 region was used to isolate genes by a number of gene identification techniques and to generate transcript maps of the region, as presented in the three accompanying manuscripts of Brody et al. (1995), Osborne-Lawrence et al. (1995), and Friedman et al. (1995).