In recent years, the field of immunology has expanded rapidly. Volume 2 of Modern Trends in Immunology presents 11 reviews, each written by an authority in the field, each dealing with a different facet of new developments. Topics pertain rapidly advancing discipline that to present day problems in clinical medicine. It is inevitable in such a rapidly advancing discipline that several presentations are incomplete, others obsolescent. The initial chapter deals with the relationship of bacterial antigens to infectious disease. Problems of isolation, identification, purification, and clinical use of vaccines of bacterial antigens are reviewed. The possible relationship of bacterial antigens to human tissue antigens is not discussed. The various types and effects of antigen adjuvants are well described in the second chapter. In view of its widespread use, the status of adjuvants in hyposensitization therapy of human atopic disease is a notable omission. The feasibility and problems involved in immunization