This paper presents a compilation of the results of patch tests made on 998 persons, who were subjected to a total of 10,198 patch tests with about 500 different substances. Before considering the results obtained, we believe it essential to discuss briefly the nature of the dermatologic material and the circumstances under which these tests were performed. It must first be emphasized that we shall not attempt to consider the merits of patch tests as a diagnostic measure; nor shall we enter into a discussion of the technic of their application, of the reading of results or of the indications for patch tests in general.1In agreement with the majority of observers, we are convinced of the value of patch tests as an aid to diagnosis, provided proper regard is given to their inherent limitations. Furthermore, it must be stated at the outset that this is not a report