Abstract: Objective To establish a stable and efficient in vitro culture model for tachyzoites of Toxoplasma gondii RH strain. Methods Tachyzoites were inoculated into HeLa cells to establish an in vitro culture system. The proliferation of tachyzoites was observed under microscope by the method of Giemsa stain. At the same time， the longterm tachyzoites maintenance in HeLa cells was established，and the effect of different temperature and time on the yield and motility of tachyzoites were observed. Results The RH strain tachyzoites were cultured and maintained in HeLa cells. Most HeLa cells were destroyed 96 h after inoculation. In the long-term culture system， the proliferation of tachyzoites was stable and its virulence to mouse showed no decrease. Furthermore， tachyzoites in this system proliferated by 5-20 times and （1-5）×10⁷ tachyzoites were harvested. When cultured in HeLa cells at 37 ℃ for 72 h then at 25 ℃ for another 120 h， the tachyzoites proliferated by more than 40 times with a motility rate of over 90%. However， rare HeLa cells left in the medium were found. Conclusion Tachyzoites of T. gondii RH strain can be subcultured in HeLa cells for a long time， and high proliferation rate of tachyzoites can be obtained from this in vitro culture system.

Key words: Toxoplasma gondii, Tachyzoite, HeLa cell, In vitro culture