A prospective, randomized, double-masked pilot study compared topical 1% ALO 2145 (p-aminoclonidine hydrochloride, a topical alpha 2-agonist) with a placebo to determine its ability to minimize any acute postoperative intraocular pressure (IOP) increase after argon laser iridotomy. Twenty-eight eyes (21 patients) with chronic narrow angle glaucoma underwent argon laser iridotomy. Fourteen eyes were treated with ALO 2145; the remainder received a placebo. All eyes received one drop of the appropriate medication one hour before and following the iridotomy. Six eyes (43%) treated with the placebo and no eyes treated with ALO 2145 experienced an IOP increase greater than 10 mm Hg over baseline. The mean IOPs and mean IOP changes from baseline were significantly lower during the first three postoperative hours in the eyes treated with ALO 2145. No significant difference was noted in the ease of iridotomy formation, rate of iridotomy closure, visual acuity, anterior segment inflammation, or mean heart rate.