Cells are known to adhere to implanted intraocular lenses (IOLs), but the mechanisms of this adhesiveness are not known. We studied cellular adhesiveness on four posterior chamber IOLs that had been implanted into monkey eyes. The animals were killed at 4 and at 7 days after lens implantation. The IOLs were removed and examined by transmission electron microscopy. At 4 days after IOL implantation, macrophages were attached to the IOL surface; at 7 days after implantation, multinucleated giant cells were attached to the IOL surface. These cells had bundles of microfilaments in the subplasmalemmal region of areas of close cell-IOL apposition. These microfilaments may play an important role in the cellular adhesiveness on the surface of implanted IOLs.