MK-927 is a water soluble, potent inhibitor of human carbonic anhydrase (CA) II in vitro. Topical administration of MK-927 reduces intraocular pressure (IOP) in rabbits. Elevated IOP was produced in cynomolgus monkey eyes by argon laser photocoagulation of the trabecular meshwork. IOP was measured at 0 hr, 0.5 hr and hourly for 8 hrs in 8 eyes for two baseline days, one day on vehicle and five days of therapy with 2% MK-927 b.i.d., after initial single-dose trials of various concentrations. IOP was not significantly different comparing baseline and vehicle treated days. Significant (p less than 0.05) reductions of IOP occurred for five days lasting at least 8 hrs after each dosing. At 3 hrs after treatment with vehicle the IOP was 31.6 +/- 3.4 (SE) mm Hg. Maximum reduction of IOP occurred at 3 hrs after application of MK-927, the IOP decreasing from day 1 (19.9 +/- 1.0 mm Hg) to day 5 (16.5 +/- 1.6 mm Hg). MK-927 appears to have great clinical potential.