We conducted a randomly assigned, double-masked, controlled clinical trial to assess the efficacy of 1% apraclonidine hydrochloride in controlling postoperative intraocular pressure increases in patients undergoing extracapsular cataract extraction. Apraclonidine hydrochloride was given either one hour preoperatively or immediately after uncomplicated, extracapsular cataract extraction with posterior chamber intraocular lens implantation and compared with artificial tears given immediately postoperatively. Those who received apraclonidine hydrochloride preoperatively had significantly lower mean intraocular pressure at the first postoperative reading (P = .0005). After preoperative and postoperative apraclonidine hydrochloride, the mean early postoperative intraocular pressure was 19.8 mm Hg and 32.0 mm Hg, respectively, and 27.6 mm Hg after artificial tears. No patient who received preoperative apraclonidine hydrochloride had an intraocular pressure increase to 30 mm Hg or higher postoperatively. Nine of 20 patients (45%) who received postoperative apraclonidine hydrochloride and eight of 18 patients (44%) who received postoperative artificial tears had an increase of intraocular pressure to 30 mm Hg or higher in the early postoperative period. These differences were also highly significant (P = .0005).