Acute elevations in intraocular pressure (IOP) commonly follow extracapsular cataract extraction and lens implant in glaucoma patients. Thirty six patients with glaucoma undergoing cataract extraction and posterior chamber lens implantation received one of three treatments. Group 1: 500 mg of Diamox Sustets (acetazolamide) 1 hour preoperatively (10 patients); Group 2: peroperative intracameral Miochol (acetylcholine) (11 patients); Group 3: the above treatments combined (15 patients). IOPs were measured at 3, 6, 9, and 24 hours postoperatively. The average of the maximum pressure rises above the preoperative level over the 24 hour period was greatest for the group receiving acetazolamide only at 8.9 mm Hg; for the acetylcholine group the average maximum rise was 6.3 mm Hg; while the combined treatment group showed a decrease of 0.7 mm Hg. IOP rises of > 6 mm Hg were seen in 7% of patients (one of 15) in the combined treatment group, 45% (five of 11) of the acetylcholine group, and 70% (seven of 10) of the acetazolamide group. IOP rises of > 10 mm Hg were seen in 7% of the combined treatment group, in 18% of the acetylcholine only group, and in 50% of the acetazolamide only group. A pressure rise > 20 mm Hg was seen in one patient receiving acetazolamide only and one patient receiving acetylcholine only. The difference between the acetylcholine group and the combined group for rises > 6 mm Hg was significant using the chi 2 test while the acetazolamide group showed a significant difference for rises > 6 and 10 mm Hg compared with the combined group. All acute pressure rises were recorded before or at 9 hours following operation except in the combined treatment patient where the rise occurred at 24 hours. To prevent the acute IOP rises seen following cataract surgery with lens implant in glaucoma patients we recommend combined ocular hypotensive therapy.