In November, 1946, an International Hematology and Rh Conference was held in Dallas, Tex-Mexico City. This volume records most of the papers and discussions presented at the conference on subjects pertaining to the Rh factor. Clinicians will be particularly interested in a paper by Chown on variations in erythroblastosis fetalis, a paper by Davidsohn on correlation of Rh antibodies clinical findings, and a paper by Wallerstein on treatment of erythroblastosis fetalis by substitution transfusion. Other reports, such as those on the relationship of the A and B factors to the Rh factor and to erythroblastosis fetalis, and a paper on a possible third order of antibodies, suggest new fields of investigation and techniques of serologic diagnosis.