Investigation of the morphology and function of lym­ phatic tissue evolved rapidly during the past few years. Many new aspects and dimensions have proved to be of gre­ at significance for the understanding of processes which are triggered by immunological means. The cellular coor­ dination that operates in immune response emphasizes aga­ in the importance of immuno-ecologic relations in the lymphatic tissue. It has become obvious that both the morphologic and the molecular properties of lymphatic cells are essential for their functional expression. Furthermore, the emerging body of evidence clearly shows that nonlymphatic cells (e.g. reticular cells and neu­ rons) and substances that exert neurohumoral and hormo­ nal activities should be regarded as normal constituents of the microenvironment of lymphatic tissue. The immune phenomena are, therefore, direct derivates of processes that occur in this microenvironment. Such a view of the microenvironment of immunity calls for immunoendocrino­ logic, immunoneurologic and immunopharmacologic projects, it stimulates the creative imagination, and encourages research workers to enter into unexplored areas of the immunosciences. This book illustrates the joint efforts made by scientists from various parts of the world and armed with different ideas and views, to solve some of the mysteries of lymphatic tissue microenvironment. The Fourth Conference took place in the lovely set­ ting of Dubrovnik and in the shade of olive trees under which philosophers used to meditate in ancient times.