The recent identification of gene mutations involved in hereditary cancers increasingly allows for predictive DNA-testing. There is an urgent need to analyse the ethical issues involved. This article concentrates on the ethics of predictive testing for mutations in the breast (and ovarian) cancer genes BRCA1 and -2. Using international guidelines for presymptomatic DNA-testing for Huntington disease and the Li-Fraumeni syndrome as a model, a provisional protocol, which entails four parts is presented: (i) inclusion and exclusion criteria; (ii) preparing for the test; (iii) informing about the results of the test; (iv) post-test counselling and evaluation. The importance of an integral education of both doctors and the public is stressed.