We used specular microscopy of the corneal epithelium to examine 29 eyes of 29 patients each wearing one of five different types of contact lenses. We compared these with 24 eyes of 24 age-matched control patients. We found patients with aphakic extended wear soft contact lenses had significantly larger cells (818 +/- 186 microns2) than all other groups; and they were significantly larger than their age-matched control group (573 +/- 174 microns2) (P less than .002). The epithelial cells of extended wear soft contact lens patients (609 +/- 97 microns2) and daily wear rigid gas permeable contact lens patients (613 +/- 103 microns2) were larger than their control group of normal young patients (513 +/- 53 microns2). The cells of daily wear soft contact lens patients (484 +/- 111 microns2) and hard contact lens patients (517 +/- 46 microns2), however, were not different from controls. This study demonstrates a statistically significant shift in mean cell area of corneal epithelial cells in patients wearing some types of contact lenses.