A review of the progress made in the study of the carcinogenic properties of chemical compounds, incorporating literature published during the triennial period between the First and Second International Cancer Congresses, was presented to the Second International Congress in Brussels, in September 1936, and was subsequently reprinted with an addendum covering most of the literature published up to the end of 1936 (231). The year 1937 has again witnessed a large output of new work in this field and this is summarised in the present report. For convenience of reference the general classification adopted in the original report has been retained and the references are numbered continuously. Chemical Relationships Group I. Cholanthrene Derivatives An interesting review of the carcinogenic properties of a number of compounds structurally related to cholanthrene was published early in the year by Fieser, Fieser, Hershberg, Newman, Seligman, and Shear (250). In the case of many of the compounds discussed the results of biological testing were necessarily of a preliminary character, and the points of view expressed may eventually require slight modification. Reference is made to some of these compounds under Group III (below). The synthesis of 4:10-dimethylene-1:2-benzanthracene, an isomeride of cholanthrene, has now been described by Fieser and Seligman (256) and the same compound was prepared by Dansi (239, 240) by a different method. This compound, when injected into rats, produces tumours of connective tissue (308); so the interesting fact emerges that of the four known isomeric “ace-1:2-benzanthracenes,” the three in which substitution occurs at a meso position of the benzanthracene molecule are all carcinogenic (cholanthrene, 8:9-dimethylene-1:2-benzanthracene, 4:10-dimethylene-1:2-benzanthracene), whereas the fourth, 3:4i-dimethylene-1:2-benzanthracene (228), in which this condition is not fulfilled, is inactive.