Objective To investigate effect of intravitreal injection of FK506 on the survival of human retinal pigment epithelial (RPE) cells heter oplastically transplanted into the subretinal space of rabbits.Methods The immortalized human RPE cells were genetically labeled by retrovirus vector carrying a green fluorescent protein (GFP). A total of 50 μl RPE cells suspension with 4×103 cells/μl which expressed GFP were injected into the subretinal space of both eyes of 18 white rabbits and 10 gray rabbits. The left eyes of all of the rabbits were injected of 5 μl FK506 (5 μg/μl) intravitreally once a week during the first 5 weeks, then once every other week until the 20th week and the right eyes were as the control. The histological sections of heteroplastic RPE cells were observed by epifluorescent microscope.Results GFP-expressing cells could be seen after 1 week, 2, 3, 4, 6, 10, 11, 14, 18, 20, 23, 24, 25, 26, 33, and 54 weeks in white rabbits and after 4 , 5, 6, 7, 14, 18, 20, and 26 weeks in gray rabbits. The configuration and integrality of the RPE-GFP cells in the left eyes which had been intravitreally injected of FK506 1-14 weeks after transplantation were better than those in the right eyes without injection. After 18 weeks, the condition of heteroplastic cells with few difference in both eyes in 7 white and 3 gray rabbits were found. After 1-6 weeks, focal and disseminated lymphocytes around the choroidal small vessles of right eyes in 6 white and 3 gray rabbits could be seen while the infiltration of the lymphocytes in the left eyes was much reduced.Conclusion Intravitreal injection of a small amount of FK506 at the first 3 months after transplantation may significantly improve the survival of heteroplastic RPE cells in the subretinal space of rabbits. (Chin J Ocul Fundus Dis，2003，19：333-404)