My purpose in this paper is to report the results of an investigation on the subject of endophthalmitis phaco-anaphylactica. The clinical material used for this study consisted of 700 unselected patients with cataract who were admitted to the Wills Hospital during 1932. THE DETERMINATION OF HYPERSENSITIVITY TO LENS PROTEIN Each of the 700 patients with cataract was first given a cutaneous test, and the test was repeated on subsequent admissions. Further repetitions of the test were made during the stay of some of the patients in the hospital whenever the situation demanded it. A total of 1,038 tests were made. Each cutaneous test consisted of a series of three injections given intradermally in the forearm after the area to be used had been cleansed with alcohol and allowed to dry. The solutions which were used were sent to me by Dr. Earl L. Burky of the Wilmer Institute and were