To determine whether immunohistochemistry can identify BRCA1 mutations, immunohistochemical (IH) analysis was undertaken on paraffin sections of paired ovarian cancer and normal tissue using antibodies against both terminal regions of the BRCA1 protein. Ten patients at risk for BRCA1 mutations were studied. The results of BRCA1 mutation analysis and IH were compared. In tumor, IH correctly identified the presence or absence of loss of heterozygosity in all specimens. In all uninvolved specimens, IH correctly identified the presence or absence of a germline mutation. The sensitivity, specificity, positive and negative predictive values were 100% suggesting promise as a rapid and inexpensive screen.