We serially examined the endothelial cellular pattern and thickness of the central cornea after intracapsular cataract extraction and penetrating keratoplasty. The endothelial cellular pattern was analyzed with a computer-assisted digitizer. We used the frequency of hexagonal cells as the index to describe the degree of hexagonality in the cellular pattern. In the intracapsular cataract extraction group (20 eyes), the frequency of hexagonal cells was 68% preoperatively. During the first four weeks this frequency decreased rapidly to a significantly lower level (52%). The corneal thickness was significantly increased within the first week (0.57 mm) and steadily decreased to preoperative values at four weeks (0.53 mm). During the period from four to 24 weeks, the frequency of hexagonal cells increased gradually to 64%. In the penetrating keratoplasty group (ten eyes), the frequency of hexagonal cells and the thickness at one month were 62% and 0.64 mm respectively. During the next six months the frequency of hexagonal cells decreased significantly to 53%, and the thickness decreased to 0.53 mm. There was a gradual increase in the frequency of hexagonal cells to 62% during the two years after penetrating keratoplasty.