partial ciliary processes argon laser photocoagulation (PCLP) in the management of glaucoma has been the subject of a carefully conducted, prospective 5+-year clinical trial in 22 eyes of 20 patients. The mean intraocular pressure (IOP) +/- SD was significantly lower (15.5 +/- 3.6 mm Hg) than before the procedure (29.9 +/- 10.1 mm Hg; 0.001 less than P less than 0.005, paired t-test). The mechanism of intraocular pressure reduction is due mainly to the reduction in the rate of aqueous humor formation with a mean outflow facility (C-value) +/- SD of 0.12 +/- 0.11 before and 0.12 +/- 0.06 microliter/min/mm Hg after the procedure. This new procedure, done on an out-patient basis, shows promise as a convenient, low-risk, and useful alternative procedure in selected glaucoma cases that are poorly controlled by medical or surgical measures. This new approach may also be used as an adjunct in the medical and/or surgical management of aphakic and ciliary block glaucoma.