The Nd:YAG laser is used primarily in the management of posterior capsular opacification in patients who have had extracapsular cataract extraction. Despite wide clinical use little is known about its damaging effects on the ocular tissues particularly on the corneal endothelium. To evaluate the pathologic changes caused by high powered Nd:YAG laser pulses on the anterior segment of the eye we focused the beam of this laser on the anterior lens capsule in rabbit eyes. Six eyes underwent anterior capsulotomy and three power settings were used (3.4 mJ, 5.8 mJ, 8.6 mJ). The fellow eyes served as controls. We studied acute corneal endothelial changes 6 hours after the capsulotomy using transmission electron microscopy. Results indicate that especially in the high setting the laser energy can cause injury and destruction of endothelial cells and alterations in the Descement membrane. These effects may be crucial of patients with corneas in critical cell number after a cataract surgery.