Forty-five adults with primary open-angle glaucoma received argon laser trabeculoplasty in two stages (180 degrees in each session) separated by one month. The indication for argon laser trabeculoplasty in each case was uncontrolled glaucoma consisting of progressive optic disk cupping and visual field loss despite maximally tolerable medication. A P value of .01 by Student's two-tailed paired t-test was used for statistical significance in the analysis of the intraocular pressure data. In most cases, the greatest reduction in intraocular pressure followed stage 1. Some patients received no additional benefit from stage 2; in other cases, the second stage was not only beneficial but provided most of the reduction in pressure. The pretreatment intraocular pressure level influenced the response to laser therapy. Patients with the highest pretreatment intraocular pressures received the most benefit. Both stages were complicated by a transient postoperative increase of 5 mm Hg or more in 12 patients (approximately 19%).