Argon laser trabeculoplasty (ALT; 1.0 W, 0.1 sec, 50 microns) was performed in right eyes, and low energy, Q-switched Nd:YAG laser trabeculoplasty (Nd:YAGLT; 1.1-4.8 mJ/pulse) in left eyes of 14 patients with primary open-angle glaucoma and in one patient with juvenile glaucoma. The pre-laser intraocular pressure (IOP) was medically uncontrollable (IOP > 21 mmHg). The interocular pressure difference varied between 0 and 3 mmHg. In 9 patients IOP decreased to less than 22 mmHg (success) in both eyes. No statistically significant difference has been revealed with paired t-test in the degree of IOP decrease between ALT and Nd:YAGLT treated eyes during the 1-18 months' follow-up. Treatment variables of Nd:YAGLT had no statistically significant effect on the duration of the post-laser success with Cox-regression. In 4 patients both treatments were ineffective (IOP > 21 mmHg). In 2 patients ALT was successful but Nd:YAGLT was ineffective. In three cases of early bilateral laser failure (IOP > 21 mmHg at the first month visit) trabeculectomy was performed on both eyes in the third post-laser month. Following ALT the uveoscleral meshwork was severely destroyed in the area of the laser spots, and the surrounding collagen fibres were heat-damaged. The meshwork between the laser spots was covered by a membrane formed by migrating endothelial cells. In the uveoscleral meshwork Nd:YAGLT induced severe focal damage surrounded by circumscript shrinkage and scarring. The juxtacanalicular tissue remained free of laser induced damage. No endothelial membrane was present. The results suggest that low energy, Q-switched Nd:YAGLT may represent an alternative method of glaucoma laser surgery.