Over a two-year postoperative period, cells on hydrogel (poly HEMA) and poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) were observed by specular microscopy. First small, round cells and fibroblast-like cells and later epithelioid-like cells and foreign-body giant cells could be seen on both IOL types. In eyes with prolonged postoperative inflammation a greater number of cells was observed and the cells remained on the IOL surface for a longer period. We found fewer cell reactions on hydrogel IOLs during the postoperative period of our follow-up. Foreign-body giant cells were observed on only 9%. These cells were smaller than those on PMMA IOLs. This finding may suggest that poly HEMA demonstrates greater biocompatibility, with regard to this foreign-body cell reaction, than PMMA. However, we found more pigment dispersion (50%) on the surface of hydrogel IOLs. These pigment deposits induced no cell reactions and there was less phagocytosis of the pigment debris. In 7% of the cases, dust-like, white precipitates of uncertain origin were seen; in 5% amorphous debris was seen. Fine scratches caused by polishing during the manufacturing process were seen in some cases. The postoperative clinical signs for PMMA and hydrogel IOLs were similar.