Objective:To detect collagen I synthesis activity in the vitreous of PVR induced by macrophages in rabbits. Methods:PC Ⅲ (Procollagen Ⅲ ) concentrations were measured by radioim- munoassay in the vitreous samples of 14 rabbit eyes with experimental PVR and 14 control eyes. Results:The mean PC Ⅲ concentration on the 7th day after macrophage injection as 257.58mu;g/L(range,236.04~266.88mu;g/L,n= 4)and significantly increased on the 14th day later. On the 28th day the mean concentration of PC Ⅲ as 912.23mu;g/L (range, 881.36~943.10mu;g/L ;n= 2). There was a significant difference between the 7th and the 14th, 21st of 28th day statistically(P＜0.05). PC Ⅲ was not detected in control eyes. Conclusion:The PC Ⅲ level in the vitreous of rabbit eyes with experimental PVR increased significantly from the 7th to the 28th day after macrophages injection and is well consistent with the time course of scarring and the development of traction retinal detachment in the PVR model. （Chin J Ocul Fundus Dis,1996,12: 43-44）