【Objective】To invest ig ate the relationship between induced dif ferentiation and regulation of telomerase act ivity in cultured osteosarcoma cells .【Methods】Osteosarcoma cells w ere t reated by dif ferent doses of retinoic acid (RA)and dexamethasone (DEX).Telomerase activity and human telomerase RNA (hTR)of treated cells w ere detected by telomere repeat amplification pro tocol (TRAP)and by No rthern blot ting analy sis . 【Results】Af ter t reatment w ith RA or DEX

the g row th of HOS cells w as inhibited .Alkaline phosphatase activity (differentiation marker of osteogenetic cells)of the cells increased significantly .Telomerase activity decreased with increasing t reatment doses and times

but the ex pression level of hTR did not change obviously . 【Conclusions】Both RA and DEX could inhibit cell grow th and induce differentiation of HOS cells.Decreasing of telomerase activity could be considered as a marker of differentiation of HOS cells

but it does not co rrelate with the expression level of hTR .