In a group of 68 patients a double-blind study was performed to assess the effect of preoperative oxybuprocaine 0.4% (Dorsacaine, Novesin) eye drops in comparison with a placebo in preventing surgically induced miosis during extracapsular cataract extraction. One drop of oxybuprocaine 0.4% or placebo was instilled 10 and 5 minutes preoperatively. The pupil diameter was recorded at different stages of the operation. It was found that oxybuprocaine reduced the amount of pupil constriction during the operation significantly as compared with the placebo group, facilitating the removal of lens material and the implantation of an intraocular lens. The effect of oxybuprocaine is considered to be due to anaesthetic action on sensory nerves in the eye, which may inhibit the release of a miotic substance.