In a consecutive series of 90 patients we examined the effect of intracameral acetylcholine and carbachol on intraocular pressure following extracapsular cataract surgery. In all cases phacoemulsification and implantation of a folded polyhema intraocular lens under healon was performed. After evacuation of the viscoelastic substance from the capsular bag behind the inserted lens and wound suturing we instilled 0.5 ml 1% acetylcholine, 0.5 ml 0.01% carbachol or 0.5 ml balanced salt solution respectively into the anterior chamber. Without the influence of antiglaucomatous drugs applanation tonometry was performed 6 and 18 hours postoperatively. When compared with preoperative values intraocular pressure decreased in the carbachol group (-2.8 mm Hg) but increased in the acetylcholine group (+0.6 mm Hg) and control group (+4.7 mm Hg). 18 hours postoperatively the mean change was -3.0 mm Hg in the carbachol group, +0.8 mm Hg in the acetylcholine group and +2.3 mm Hg in the control group. Intraocular pressure exceeding 22 mm Hg at 6 hours was observed in 33% of the control group and 13% of the acetylcholine group but none of the carbachol group. At 18 hours intraocular pressure was still elevated in 13% of the control group, 10% of the acetylcholine group and 3% of the carbachol group. Reviewing our results we conclude that the evacuation of viscoelastic substances from the capsular bag behind the implanted lens reduces the incidence of pressure rises in the early postoperative period. This effect can be enhanced by the use of acetylcholine and, the more potent, carbachol.