Thirty four trabeculectomy specimens from open angle glaucoma patients who had under argon laser trabeculoplasty as part of their treatment, were studied by scanning electron microscopy. Three of these were also examined by transmission electron microscopy. The intervals between laser therapy and surgery ranged from one month to five years. A sub-group consisted of six patients who had received laser treatment on more than one occasion prior to surgery. Electron microscopy revealed distortion of trabecular beams, loss of trabecular endothelial cells and the development of a cellular sheet extending from the region of Schwalbe's line and covering the anterior surfaces of the anterior portion of the uveal meshwork. The sheet occluded the trabecular spaces of the region; thus, when extensive, contributing to laser trabeculoplasty failure. It is concluded that argon laser trabeculoplasty induces a repair process, in the form of repopulating a cellular deficient meshwork, but which can become detrimental as a consequence of its success.