The toxicity and duration of octafluorocyclobutane (C4F8) injected into the anterior chambers of rabbits were compared to those of the same volume of air or sulfur hexafluoride (SF ). A volume of 0.15 ml of C4F8 or SF6 caused increased intraocular pressure, leading to buphthalmos and transitory corneal opacification. Smaller volumes of these gases or 40% mixtures of these gases with air caused minimal toxicity to the anterior chamber structure. The C4F8 consistently lasted longer than SF6 or air.