Brimonidine tartrate of 0.5% was identified as the most effective and safe dose for acute intraocular pressure (IOP) lowering. The efficacy of brimonidine tartrate 0.2% in preventing IOP elevation after an argon laser trabeculoplasty (ALT) was evaluated. Eighty patients were selected for a randomized, prospective study. Each patient was assigned to one of four treatment regimens: (1) brimonidine before and after ALT(B/B), (2) brimonidine before and placebo after ALT(B/P), (3) placebo before and brimonidine after ALT(P/B), (4) placebo before and after ALT(P/P). IOP elevation of 5 mmHg or greater occurred in 3.3% (2/60) of brimonidine-treated patients and in 30% (6/20) of placebo-treated patients. There was a mean decrease of IOP from baseline during the first 3 hours after ALT in all brimonidine-treated groups (7.1±3.4, 6.2±4.4, 3.5±2.9 mmHg for the B/B, B/P, P/B groups), but no change of mean IOP in the Placebo-treated group. Only one drop of brimonidine tartrate of 0.2% installed either before or after ALT was sufficient to prevent post-ALT IOP spike and minimize the undesired systemic adverse effects that two drop installation can produce.