Collagen shields are fabricated from dissoluable porcine scleral tissue and have been used as an ocular drug delivery system. The aim of the present study was to determine the time and extent of shield absorption when implanted sub-conjunctivally, and the absorption and release of 5-fluorouracil in vitro. Thirty New Zealand white rabbit eyes were employed. BioCor 72 hour collagen shields were surgically implanted in the subconjunctival space. Rabbits were sacrificed at 7, 14 and 21 days after shield implantation, and the remaining shields removed. Remaining shields were measured by both dry weight and protein assay. The absorption and release of 5-FU from collagen shields was determined in vitro using tritiated 5-FU. The collagen shields were not fully absorbed for at least 14 days in the subconjunctival space. In vitro, 5-FU absorbed by the shields reached saturation levels at approximately 15 minutes. Nearly 100% of the 5-FU was released within 15 minutes. Although the time for subconjunctival shield absorption may be useful for antifibroblast drugs, the rate of 5-FU release from these shields is not optimal for enhancing bleb formation when shields are soaked in solutions of 5-FU.