In this paper, we describe the physical map and transcriptional organisation of a 100-kb region with the BRCA1 locus at 17q12-21. Using the cDNA of the EDH17B2 gene as a probe, we screened a human genomic cosmid library. Positive cosmid clones were aligned and a contig around the EDH17B2 gene was established, expanding the previously reported map. In order to identify genes located in this region, we used the cosmid inserts to select cDNAs from a human ovarian cDNA library. Among the clones identified, cDNA OV-1 corresponds to a human homologue of a rat PRL-1 tyrosine phosphatase gene that shows enhanced expression during hepatic regeneration and in some tumour cell lines. Neither the OV-1 nor the PRL-1 protein shares strong homology with any previously characterised phosphotyrosine phosphatase, suggesting that they probably belong to a new phosphatase family. In an attempt to characterise the OV-1 gene, we found that the genomic sequence present on chromosome 17 probably corresponds to a nonfunctional copy of the gene, as it contains several sequence changes that disrupt the potential coding information of the gene. Three other cDNAs, corresponding to unrelated genes, were also identified and characterised. They did not reveal striking homologies in database sequence comparison and therefore represent new genes localised on chromosome 17q, in a region that frequently shows loss of heterozigosity in sporadic breast and ovarian cancers.