The realization of essential cellular'interactions in the immune response convokes a better understandin~ of the fixed and free cellular components of lymphatic tissue. Ger~inal centers of lymphatic tissue have long been considered to have a funda~ental role in the immune reaction, and have been suspected of being topographic regions where so~e of these essential cellular inter- actions may occur. The physiological significance of these topo- graphic regions in lynphatic tissue is only now becoming clarified from recent studies of antigen localization, but the histo2enic relation of the cellular compartments still needs to be resolved. This book represents the Proceedings of the Second International Conference on Lymphatic Tissue Germinal Centers, held at the University of Padova, Padova, Italy, June 26-28, 1968. The aim of the ~eeting was to bring together current infor~ation on the physiological significance of germinal centers in ly~rhatic tissue and their possible role in the immune response. The range of interests extended from phylogenesis and ~orphology to studies of antigen and viral localization, cytokinetics and cytodifferen- tiation, immunochemistry, and im~unosuppression. The interactions of central lymphoid organs, such as the thymus and bursa, are studies having an essential role in these Proceedings. Also, several studies deal with lymphatic tissue germinal centers in delayed hypersensitiv- ity and neoplastic disease. The effects of immunosuppressive drugs, antilymphocyte serum, radiation and hormones on lymphatic tissue and germinal centers are also areas covered in these Proceedings.