The effect of an antiprostaglandin, piroxicam, in preventing surgically induced miosis is studied. Patients undergoing extracapsular cataract surgery were randomly divided into the piroxicam and placebo groups. Intra-operative measurements of the pupillary diameters were performed. The stages of procedure at which they were measured were at the beginning of operation (Stage 1), after anterior capsulotomy (Stage 2), after lens nucleus delivery (Stage 3) and at the end of irrigation and aspiration (Stage 4). It is noted in this Study that the pupillary diameters were larger at stages 2,3 and 4 in the piroxicam group. The increase in the mean pupillary areas of the piroxicam group were statistically significant for Stages 3 and 4.