BRCA1 and BRCA2 mRNA expression in sporadic breast cancers was quantified by a real-time reverse transcriptase-polymerase chain reaction (RT-PCR), and the relationship of their expression with various clinicopathological factors was studied. BRCA2 mRNA levels (0.993 +/- 1.395, mean +/- SD (BRCA2 / beta-glucuronidase mRNA ratios)) were significantly (P < 0.01) higher than BRCA1 mRNA levels (0.519 +/- 0.570 (BRCA1 / beta-glucuronidase mRNA ratios)), and a weak but significant (r = 0.390, P < 0.01) correlation was observed between BRCA1 and BRCA2 mRNA expression levels. There was no significant association between BRCA1 mRNA expression and clinicopathological factors such as menstrual status, tumor size, lymph node status, estrogen and progesterone receptor status, and histological grade. On the other hand, there was a significant association between higher BRCA2 mRNA expression and estrogen receptor (ER) negativity (P < 0.01) or progesterone receptor (PR) negativity (P < 0.01) or high histological grade (P < 0.01). These results suggest a differential contribution of BRCA1 and BRCA2 in the pathogenesis of sporadic breast cancers. BRCA2 mRNA is speculated to be up-regulated in response to proliferation and genomic instability in high histological grade tumors.