Germ line BRCA1 and/or BRCA2 mutations were screened in 50 Turkish breast and/or ovarian cancer patients composed of hereditary. familial, early onset and male cancer groups. Genomic DNA samples were tested by heteroduplex analysis and DNA sequencing. Two truncating BRCA2 mutations, one novel (6880 insG) and one previously reported (3034 delAAAC), were found in two out Of six (33%)) hereditary breast and or ovarian cancer patients. A novel truncating (1200 insA) and a missense (2080A-->G) BRCA1 mutation was found in two of 27 (7%) individuals in the early onset group. A total of four (8%) disease-causing mutations in 50 breast cancer patients were identified in BRCA1 and BRCA2 genes. In addition, five BRCA1 sequence variants have been identified in 23 patients. These results indicate that BRCA1 and BRCA2 genes are involved in some, but not all, forms of hereditary predisposition to breast cancer in the Turkish population. (C) 2000 Published by Elsevier Science Ltd.