OBJECTIVES: To develop a real-time quantitative RT-PCR method for BRCA1 mRNA and then use it for the study of BRCA1 gene expression in human MCF-7 breast cancer cells after their exposure to antineoplastic agents and gamma irradiation. DESIGN AND METHODS: The developed QRT-PCR method is based on the real-time monitoring of a fluorescein-labeled TaqMan probe, specific for BRCA1 mRNA, during PCR in the LightCycler. A BRCA1 PCR amplicon was purified, quantitated and used as a standard of known concentration for the development and analytical evaluation of the assay. The method was applied to study the alteration of BRCA1 gene expression after exposure to taxol, doxorubicin, 5-fluorouracil, etoposide or gamma irradiation in human MCF-7 breast cancer cells. RESULTS: The developed method is quantitative, highly specific for mRNA and highly sensitive (detection limit of 4 BRCA1 copies per mug of total RNA). We observed a reduction of BRCA1 expression for all antineoplastic agents used, while the gamma irradiated MCF-7 cells had an increase of expression with a peak at the 10 Gy dose. CONCLUSIONS: The developed BRCA1 QRT-PCR method is quantitative, highly sensitive and specific. The proposed method is rapid, automated, and cost effective and can be used to study BRCA1 expression in a variety of clinical samples