Purpose:To determine the efficacy of a low-molecular-weight heparin (fraxipparine) administered in the infusion fluid to prevent postoperative fibrin formation in a rabbit lensectomy and vitrectomy model. Methods:Fourteen adult pigmented rabbits were randomly as signed into two groups.Standard fragmatome lensectomies and core vitrectomies were performed prospectively in a masked fashion on control eyes with balanced salt infusion and on experimental eyes treated with fraxiparine/ml 6U in the infusate.Intraoperative bleeding was graded in a masked fashion by the surgeon. The amounts of firbrin and hemorrhage were graded in a masked fashion on postoperative days 1 through 7. Results:The mean grde of fibrin in the eyes treated with fraxiparine was lower than that in the control eyes (Plt;0.01) on postoperative days 1 through 3 respectively.Also,the average days to clear the fibrin in the eyes treated with fraxiparine was shorter than that in the control eyes (P＝0.001).No statistically significant differences in the degree of intraoperative or postoperative hemorrhage were noted between the two groups. Conclusion:Low-molecular weight heparin(fraxiparine) is an effetive inhibit or of postoperative fibrin formation in a rabbit model and is not associated with is not associated with an increased risk of intraoperative or postopertive bleeding at the tested dose. (Chin J Ocul Fundus Dis,1998,14:35-37)