THC-YAG laser sclerostomy was performed in 7 eyes of 6 monkeys. The 26-gauge optic probe, which delivers energy perpendicularly to the long axis of the probe, was inserted through a 1-mm conjunctival stab incision, 6-7 mm away from the limbus, and the probe tip was positioned at the sclerostomy site. Pulse energy of 80 mJ or 100 mJ was used with a repetition rate of 5 pulses per second. Total energy levels to produce a new outflow pathway ranged from 1.2 to 6.6 J (2.8 +/- 1.2 J). After the surgery, 5-fluorouracil (0.1 mg daily) was injected subconjunctivally for 7 days, and intraocular pressure measurements and ophthalmic examination were performed for 4 weeks. Eyes were enucleated just after surgery or 1 week or 4 weeks after surgery. Intraocular pressures in operated eyes at 1 week and 4 weeks after surgery were reduced to 7-10 (9 +/- 1.2) mmHg, and 0-11 (3.5 +/- 4.3) mmHg, respectively, in comparison with intraocular pressures in nonoperated eyes. Histological examination revealed that the sclerostomy hole with a diameter of 150 microns just after surgery had narrowed at 1 week, and was closed by subconjunctival proliferative tissues at 4 weeks after surgery.