The changes in intraocular pressure (IOP) following peritomy and wet-field coagulation of 10 rabbit eyes and 7 human cataractous eyes were investigated. The IOP difference before and after 180-degree and 360-degree wet-field coagulation on rabbit eyes showed an average increase of 11.0 ± 5.8 mmHg and 25.8 ± 7.1 mmHg(mean ± SD), respectively (p < 0.05, p < 0.01). The IOP of both groups in rabbit eyes were elevated for 2 to 3 days postoperatively and then became normal by the 7th postoperative day. The IOP difference before and after 180-degree peritomy and wet-field coagulation in human cataractous eyes showed an average increase of 8.4 ± 5.8 mmHg(mean ± SD)(p < 0.05). The outflow facility was poor immediately following wet-field coagulation but then improved gradually by means of tonography and concentration changes of anterior chamber neutral-red. Histologically, there was endothelial cell damage, congestion, and red blood cell extravasation of the episcleral and intrascleral vessels at one day after wet-field coagulation in the light microscopic findings. Recanalization of the episcleral and intrascleral capillaries was noted 3 days after wet-field coagulation and was completed 3 weeks after wet-field coagulation. There was poor plastic infusion through the trabecular spaces in the one-day postoperative group compared to the control group by scanning electron micrograph. In conclusion, we have to bear in mind the possibility of an IOP rise after wet-field coagulation following peritomy for cataract and retinal surgery.