Intraocular pressure (IOP) was measured 4 to 6 hours after surgery and on the first postoperative day in 35 eyes of 35 consecutive patients undergoing initial trabeculectomy. In 27 eyes, the anterior chamber was re-formed at the completion of surgery with balanced salt solution, and in eight eyes it was reformed with hyaluronate sodium. A total of six eyes (17%) had an IOP of 40 mm Hg or greater 4 to 6 hours after surgery. Patients who received hyaluronate to maintain the depth of the anterior chamber had a significantly greater chance of experiencing a marked postoperative IOP rise, both at 4 to 6 hours (P = .005) and on the first postoperative day (P = .0038). There was no correlation between the postoperative IOP rise and the patient's age, sex, glaucoma diagnosis, preoperative IOP, use of 5-fluorouracil, or the number of sutures used to close the scleral flap. Hyaluronate may contribute to an early increase in IOP that could result in further visual field loss in eyes with severe glaucomatous damage. We recommend early monitoring of IOP after trabeculectomy and avoiding the routine use of hyaluronate.