Backgrounds: In the proriferative diabetic retinopathy, the formation of new blood vessel occurs only in the microvasculature and is marked by dissolution of the capillary basal lamina followed by migration and proliferation of distinct endothelial cell populations in response to angiogenic factor. IGF- I is known to increase retinal endothelial cell motility and rate of multiplication. This study was undertaken to determine whether IGF- I could increase the production of prtease. Methods: Bovine retinal endothelial cells were plated under subconfluent growth conditions far 48 hours using minimal esaential media (MEM) containing 10% fetal calf serurn. The cultures were washed and replenished with serum free MEM containing either 100 ng/ml or 200 ng/ml IGF I for 24 hours. For the detection of plasminogen activater production, the culture media was removed, and the cells washed with PBS and over- layed with PBS containing 0,8% agarose, 1. 3% casein and 0 003% plasminogen. Plasminogen activator activity was revealed by the develapment of clear zones, representing plasmin-mediated caseinolysis of the opaque indicator gel. Results: The amount of lysis present with 200 ng/ml of IGF- I was of the same magnitude as that detected with the known tumor promoter, phorbol myristate acetate at a concentration of 80 ng/ml. Conclusion: lGF- I in addition to act as stimulating endothelial cell multiplication and chemotaxis, also stimulates protease production. This strongly suggests that IGF- I may function as an angiogenic factor.