OBJECTIVE To compare the influence of low-molecular-weight viscoelastics on postoperative intraocular pressure (IOP) and corneal endothelial cell loss after phacoemulsification METHODS Sixty-nine eyes undergoing phacoemulsification surgery were randomized to have either Opegan (Santen Pharmaceuticals, Osaka, Japan) alone or the soft-shell technique using Viscoat (Alcon Surgical, Fort Worth, TX) during phacoemulsification. The IOP was measured preoperatively and at 5 and 24 hours postoperatively. Intraoperative factors and corneal endothelial cell loss were also examined. RESULTS Mean IOP was increased at 5 hours after surgery but returned to preoperative levels at 24 hours in the Opegan group, whereas it remained higher at 24 hours than at preoperative levels in the soft-shell group. When comparing groups, IOP at 5 and 24 hours postoperatively in the Opegan group was significantly less than that in the soft-shell group. Corneal endothelial cell loss was approximately the same in the two groups. CONCLUSIONS The increase in IOP following phacoemulsification surgery with the use of Opegan was less than that with the soft-shell technique using Viscoat, although endothelial injury was almost the same.