We performed a morphologic investigation of the corneal endothelium following in vivo excimer laser ablation at 193 and 248 nm in rabbit eyes. Control experiments were performed in eyes with incisions of similar depth made with a diamond surgical knife, and normal control eyes were studied in parallel. We found that 193-nm excimer laser incision to 90% of corneal depth produces endothelial alterations similar to those seen underlying diamond knife incisions of similar depth. Scanning electron microscopy revealed an incisional ridge and endothelial cellular edema; endothelial cell loss was not observed. In contrast, 248-nm ablations of similar depth and energy density revealed loss of underlying endothelial cells and a surrounding zone of severe cellular damage.