Both short- (1 week) and longer-term (7 week) studies have been made on a series of silicone oils to determine their effects on blood-retinal barrier permeability. About 25% of the vitreous humor was replaced with the test oil, and fluorophotometric determinations made after intravenous fluorescein at intervals after oil injection. The short-term studies revealed a uniform disturbance of the eye at 24 hours after oil injection that probably represents the physical disturbance of the eye during injection. For most oils the readings on day 4 and day 7 after oil injection revealed no difference between the experimental and the paired control eye. Adatomed 5000 cps oil and a Japanese 1000 cps oil caused more sustained aqueous humor fluorescein values over the first week. Longer-term studies, with two oils shown in prior studies on corneal endothelium to increase permeability and one oil that had no influence on endothelial permeability, revealed no effects on fluorescein penetration into any ocular compartment. It is apparent that the corneal endothelium offers a more sensitive paradigm for examining the toxicity of oils for predictive behavior of long-term exposure of the retina.