Posterior chamber intraocular lenses (IOLs) were implanted in cat eyes after extracapsular cataract extraction or phacoemulsification. Various degrees of iris and IOL contact occurred. In 52% of the eyes in which contact was present, there was associated fibrovascular membrane formation, which was statistically significant when compared to eyes in which there was no iris-IOL contact. The eyes were examined histopathologically; proliferation of anterior cuboidal cells, as well as a fibrous response within the stroma, was noted in eyes with the most extensive contact. Human clinical correlates are discussed. This study demonstrates experimentally that the iris will not tolerate significant prolonged IOL contact.