Initial screening for mutations involved a whole gene assessment using single strand conformational polymorphism (SSCP) analysis and protein truncation testing (PTT) of exon 11 in each gene. All mutations were confirmed, in both orientations, by direct fluorescent sequencing of the appropriate exon. We excluded one exon 13 duplication and two exonic deletions detected on screening 95 BRCA1 negative breast/ovarian families. A further two exon 13 duplications in five subsequent BRCA1 negative breast/ovary families originating from east of the Pennines were also excluded. Of the non large-scale rearrangement mutations, 26/78 (33%) were detected outside the commonly screened regions of BRCA1 (exons 2, 11, 20) in the UK (table 1). Similarly 15/50 (30%) BRCA2 mutations were detected outside exons 10 and 11.