This prospective study was undertaken to assess the biocompatibility of different intraocular implants and to determine factors influencing cellular reactions on intraocular lenses (IOLs). Cellular reactions seen on the surface of 653 IOLs have been documented by specular microscopy. Various types of IOLs were used with different surgical procedures in humans. The 11 lens types used fall into five groups of materials: polymethylmethacrylate (PMMA), heparin surface-modified PMMA, surface-modified PMMA, poly Hema and silicone. Factors influencing the cellular reaction on intraocular implants were elaborated on in this study. Besides the foreign-body reaction itself, cellular reactions were influenced by an increased inflammatory disposition, surgical trauma, peri-operative treatment, implant positioning and lens style. A significant correlation was found between the development of posterior synechiae and the existence of giant cells on the anterior lens surface. The incidence of cellular reactions on IOLs revealed significant differences specific to lens and material. Hydrophilic surfaces show cellular reactions in a lower percentage of cases compared with hydrophobic surfaces. An accurate and individual selection of lens material and style is mandatory to guarantee optimal after surgery.