MK-927 is a new topical carboanhydrase inhibitor with proven ability to lower intraocular pressure in glaucoma patients. Subjective and objective symptoms following topical application of MK-927 were evaluated in a randomized double-blind, placebo-controlled study in which 24 healthy male volunteers took part. Symptoms were rated according to a visual analog scale by the volunteers and according to a grading scale by the examiner. The study showed good local tolerance of MK-927, comparable to that of Betaxolol.