OBJECTIVE One of the important points in extracapsular cataract extraction with posterior chamber intraocular lens implantation is to maintain mydriasis during the intervention. In this study we compared the efficacy of two topical nonsteroidal anti-inflammatory drugs: diclofenac sodium (Naclof) and indomethacin used before cataract surgery to inhibit surgically induced miosis. METHODS Sixty-four patients were operated (ECCE with IOL) by three experienced surgeons. All patients received dilatating drops and nonsteroidal anti-inflammatory drugs every 30 minutes in five doses beginning 2.5 hours before surgery. 32 patients received diclofenac sodium and 32 patients indomethacin. Pupil diameters were measured three times: first--just before the initial limbal incision, second--at the end of cortical aspiration and the last after implantation of an intraocular lens. RESULTS In both groups the surgical manipulations induced a decrease in pupil diameter but more in the group treated with indomethacin. CONCLUSIONS Diclofenac sodium appeared to be more potent than indomethacin in maintaining intraoperative mydriasis during cataract surgery.