This monograph is limited to a discussion of the isolation, composition, structure, properties and assay technics of the various estrogenic substances. After a brief outline of the work of the various investigators in this field there is a large section devoted to the author's own investigations. The purpose of the monograph is to compare the activity of the various estrogens under different conditions of administration, i. e. subcutaneous or oral, in oil or water solution, single or multiple injections. These are discussed in great detail, as can be judged by the fact that the author presents twenty-nine charts and 141 tables of his protocols. From a practical point of view this monograph can be summarized rather briefly. There is little here to interest the physician not specializing in this field.