OBJECTIVE:To verify the safe dose of cephradine in intravitreal injection. METHODS:After injecting different doses of cephradine(100mu;g,200mu;g,250mu;g,300mu;g,400mu;g)into vitreous cavity of different group of rabbits the activities of the retinal enzymes (SDH,LDH )on different time (Id,3d, 7d ) were determined respectively, and the histological and ultrastructural changes of retinas were also observed simuhaneously. RESULTS:The activity of rellnal SDH and LDH was found to be decreased gradually with tbe icreasing of the dosage of intravitreal cephradine. The activities of SDH and LDH were found in the lowest level on tile 3rd and lsl day,but they recover to normal levels on tile 7th day after intravitreal in}eetion in 100mu;g,200mu;g groups,and still lower tban normal in the other groups. Histologically,retinal edema was found both in 100mu;g and 200mu;g groups,but degradation of retinal cells,and loss of cones and rods were round in the 250mu;g, 300mu;g and 400mu;g groups. CONCLUSION: The safe dose of intravitreal injection of cepbradlnc is 200mu;g. （Chin J Ocul Fundus Dis,1997,13:139-142 ）