We performed a randomized, prospective study to evaluate the effect of intraoperative, intracameral carbachol or acetylcholine on early postoperative intraocular pressure(IOP) after extracapsular cataract extraction(ECCE) and posterior chamber lens(PCL) implantation. Fifty-six eyes of 56 patients scheduled for routine ECCE and PCL implantation were randomly assigned into three groups: (1)carbachol infusion (19 eyes) (2) acetylcholine infusion (15 eyes) (3)balanced salt solution (BSS) infusion (control, 22 eyes). We compared the preoperative IOP, early postoperative IOP, postoperative 24 hours IOP and postoperative 1 week IOP. In the measurement of early postoperative IOP, IOP was measured at least twice at 3, 6 or 9 hours postoperatively. There was no significant difference in IOP between the three groups preoperatively, at postoperative 3 hours, and 1 week. At postoperative 6 hours, both the carbachol infusion group and acetylcholine infusion group were significantly different from the BSS infusion group. At postoperative 9 and 24 hours, only carbachol infusion group had a significant difference from BSS infusion group in suppression of postoperative IOP increase. Our results suggest that intraoperative, intracameral administration of carbachol or acetylcholine prevents early postoperative IOP increase, and that carbachol has a more lasting effect.