Rabbit eyes were irradiated with a neodymium-yttrium-aluminum-garnet (Nd-YAG) laser and the changes in prostaglandin E and protein levels in the aqueous humor were measured. Intraocular pressure and pupil diameter were also determined in the same rabbits. Prostaglandin E and protein in the aqueous humor were increased depending upon the number of laser lesions. The increase in intraorular pressure and the decrease in pupil diameter occurred at similar dosages of laser irradiation. The response of the iris to the photodisruption was rapid. Changes in prostaglandin and protein contents and pupil diameter were already prominent 15 min after laser irradiation. Indomethacin pretreatment abolished most of these responses, suggesting that acute reactions following photodisruption were largely dependent on prostaglandin synthesis in iris tissue