We studied the intraocular pharmacokinetics of dorzolamide hydrochloride eye drops and the effect of dorzolamide on carbonic anhydrase activity and localization in ocular tissues. Carbonic anhydrase activity was detected in normal ocular tissues. The activity was inhibited in corneal endothelial cells, the ciliary body, lens epithelial cells, or the retina 1 to 8 hours after instillation of dorzolamide eye drops. In lens epithelial cells and the retina, the enzyme activity had not recovered even 10 hours after instillation of the drug. Immunostaining did not reveal any differences between the group administered dorzolamide eye drops and the control group administered a physiologically balanced solution. Time-related changes in dorzolamide concentrations in ocular tissues were measured by high-performance liquid chromatography (HPLC). In the cornea, anterior aqueous, iris, ciliary body and retina, drug concentrations increased 15 minutes after the instillation and peaked within 1 hour. These results suggest that dorzolamide immediately suppresses carbonic anhydrase activity in ocular tissues, and is rapidly distributed among the tissues of the eye when administered as eye drops.