Objective To test the effects of large amount of blood in the vitreous on electrophysiological examination. Methods The reductions of transmission of flash light through a serial dilution and depth of whole blood were measured.An experimental model of vitreous hemorrhage in rabbits was established by injecting 0.5ml autologous uncoagulated whole blood into the vitreous cavities after compression with an expanding perfluoropropane gas bubble.Pars plana vitrectomy was performed to clear the blood clots 2 weeks after blood injection.Ganzfeld and bright-flash electroretinography were performed through six-week observation period. Results Blood reduced remarkably the transmission of reduced remarkably the transmission of bright-flash light.Massive vitreous hemorrhage had a dense filtering effect and extinguished the Ganzfeld but not the bright-flash electrotetinogram.About 3.5log units higher of the intensities of bright- flash light than that of conventional method could stimulate the responses of ERG-B waves in blood injected eyes.Slow recovery of Ganzfeld ERG-b waves after vitrectomy were noted within 2 weeks (Plt;0.05),AND ERG-b wave reached at 80-90% of normal level during the third week. Conclusion The ERG-b waves,which become undetectable because of absorption of the dense opacities of the absorption of the dense opacities of the vitreous in eyes with a large amount of vitreous hemorrhage,can be recorded in bright-flash light conditions with nearly nearly normal amplitudes.This result indicates that functions of retina were not severely damaged by the large amount of vitreous hemorrhage. The injection of large amount of blood into vitreous cavities may cause a transient reduction of the amplitudes of ERG-b waves. (Chin J Ocul Fundus Dis,1998,14:104-107)