['To investigate telomerase activity of MCF-7 mammary cancer cells during apoptosis induced by sodium butyrate (SB) in vitro and its mechanism.', 'The proliferative activity of MCF-7 cells was assessed by morphology and MTT assay. Cell apoptosis was confirmed by DNA fragmentation and phosphatidylserine (PS) externalization. Telomerase activity was examined by TRAP-ELISA. The expression status of telomerase subunits was analyzed by RT-PCR.', 'A time- and dose-dependent inhibition was detected in MCF-7 cells treated with SB. At 72 hr after SB (2.5 mmol/L) treatment, MCF-7 cells were apoptotic with a rate of 84.3% by flow cytometric assay (AnnexinV/PI double staining). Apoptosis was also confirmed by DNA fragmentation. Telomerase activity and expression level of hTERT, the key subunit of telomerase, decreased at 24-hour time point after SB treatment. No significant changes were observed in the expression of hTR and hTP, the other two subunits of telomerase.'] Does [ Changes in telomerase activity decrease in MCF-7 cells during apoptosis induced by sodium butyrate ]?