Purpose To establish orthotopic heterotransplanted model of retinoblastoma(RB)into the vitreous cavity of nude mice for experimental studies of gene therapies in vivo. Methods To prepare the concentrated cell suspensions of human RB cell line HXO-Rb44 and inject them into the vitreous cavities of 10 nude mice(20 eyes).The experimental mice were randomly divided into 2 groups:the first group,5 mice (10 eyes) were injected with 5 mu;l of the cell suspensions,and the second group,5 mice (10 eyes)with 10 mu;l．The transplanted RB was observed by inspection and ophthalmoscopy,and graded semi-quantitatively in vivo.Light and electrone microscopes were used for histopathological examination,ABC immunohistochemical methods for NSE and GFAP,and flow cytometric investigations for DNA index(DI) and s-phase fraction (SPF). Results All of the models of RB were successfully established by injecting the cell suspensions of human RB cell line into the mice vitreous cavities.The immunohistochemical reaction of the transplanted tumor cells to NSE was positive,and negative to GFAP．The DNA index was found to be more than 1.1,and the determination of SPF indicated the presence of proliferative ability of the transplanted RB cells. Conclusion The above findings reveal that the transplanted tumor cells were similar to those of the parent cells,hence the orthotopic heterotransplantation of RB via nude mice vitreous cavity injection is a superior method in establishing the animal model for the further experimental studies of gene therapies in vivo. (Chin J Ocul Fundus Dis,1998,14:144-148)