THE PURPOSE of this paper is to evaluate the clinical merit of the commonly available mydriatics as to such factors as safety, speed of action and return to normal pupillary size. All drugs used in medicine have a range of dosage depending in part on the age of the patient and on whether the clinician desires the minimal or maximal effective dose for the patient in question. The same is true of drugs used in ocular diseases except that in ophthalmology particular care should be exercised when mydriatics are used. The initial evidences of overdosage of any drug are not usually disastrous, and the discontinuation of the drug ordinarily leads to complete return to normal in a short time. This tendency does not prevail with mydriatics. The use of a mydriatic in a patient with "potential glaucoma" may terminate in a serious complication, with a blind eye as a result.