The Third International Conference on Lymphatic Tissue and Germinal Centers in Immune Reactions was held at the University of Uppsala in Sweden, September 1-4, 1970. The conference is obliged to Professor K. E. Fichtelius for his initiative in establishing the meeting, as well as for the assistance of his staff at the Department of Histology in organizing the meetings.At the University of Uppsala inquiries into the lymphatic system go back to the 17th century and are marked by milestones, such as Olof Rudbeck's discovery of the thoracic duct in 1651 and August Hammar's fundamental work on the thymus in the beginning of this century. So one is justified to say that the conference gathered on historical ground. The organizing committee, naturally, hopes that the achievements presented at the conference will contribute to and provide significant advances in the history of lymphatic research.The material presented in this volume displays a great diversity of methods and the ingenuity of different investigators in their experimental designs. It is also apparent that contemporary research on lymphatic tissues or cells no longer recognizes the artificial borderline of morphologic versus functional. It has become a multidisciplinary affair in which an increasing number of different specialists are working closely together. Apparently this is one reason why so many new and important discoveries have been made recently.Primarily, the proceedings - as should be - reflect the communications between and the achievements of a representative sample of investigators who are using different tools in their research on the lymphatic system. Also, the ascertainment value of this sample is probably very high. Nevertheless, several sections, such as those dealing with phylogeny and ontogeny of immune response, regulation of lymphoid function, cancer immunology and immunosuppression, should be of interest to a broader audience of biologists, physicians and clinical research workers.