Glaucoma was induced in cynomolgus monkeys by photocoagulating the trabecular meshwork with the argon laser. Repeat treatments were often necessary and wide intraocular pressure fluctuations were characteristic. Baseline intraocular pressure was measured with a calibrated pneumatonometer hourly for six hours. On a succeeding day a baseline measurement was made, 50 microliter of the drug to be tested applied, and six hourly measurements of intraocular pressure repeated. The effects on intraocular pressure of timolol, epinephrine, pilocarpine, vanadate, prostaglandin F2 alpha (PGF2 alpha), forskolin, and corynanthine were tested in at least eight eyes. Significant (p less than 0.05) reductions of intraocular pressure were produced by 0.5% timolol, 2% epinephrine, 4% pilocarpine, 1% vanadate, 500 micrograms of PGF2 alpha and 1% forskolin. Five per cent corynanthine produced no significant lowering of intraocular pressure. Tonography revealed an increased outflow facility associated with the reduction of intraocular pressure 2 hours after the administration of 4% pilocarpine. This glaucoma animal model may be useful in investigating agents that lower intraocular pressure by a variety of mechanisms.