Eighty-four eyes received 107 argon laser trabeculoplasty treatments at Beth Israel Medical Center between 1982 and 1984 for advanced primary and secondary glaucoma. The prelaser mean pressure was 20·25 mmgHg. Pressures taken 1 1/2 hours postoperatively varied widely: the pressure rose after 47 treatments and fell or remained the same after 60. Significant increases in pressure occurred in 10 eyes, after 12 treatments; 42% of these had received burns of 0·8 watts or greater. Pressure changes were correlated with laser burn energy level. Both patients who had significant increases in pressure initially were retreated again - in the same eye - at another time had similar increases in postoperative pressure again, even with lower energy levels. Comparison with the results of previous reports highlights the advantages of limited treatment to the anterior trabeculum with low energy levels.