A series of rabbits have been operated upon utilizing two extracapsular techniques. An intraocular lens cast from several silicone materials was placed in each eye with the exception of one (number 9). 2. The eyes from these animals have been evaluated by clinical and microscopic techniques (including scanning electron microscopy). 3. From this limited study, it would appear that an intraocular lens made from cast silicone does not remarkably affect the physiological function of the rabbit eye. 4. Electron microscopic studies on some of the lenses in this series indicates no particular cellular reaction to or upon these lenses evaluated by this technique.