The pharmacological study of the effects and changes in a living body induced by the administration of foreign substances is a relatively neglected chapter in ophthalmology. Most handbooks of ophthalmology omit it entirely, so that the considerable knowledge concerning the role of pH, osmotic pressure and other physical and chemical characteristics of ophthalmic drugs has not found much application clinically. The present paper attempts to point out the fundamental pharmacological principles, on the use of local agents in ophthalmology. The succeeding studies will be dedicated to the sulfa drugs and antibiotics, to autonomic drugs, vitamins, disinfectants, and anesthetics. A strict order, as in a handbook, will not be attemped, as the purpose of these studies is to furnish exhaustive information concerning isolated problems rather than a complete system of pharmacology.