This volume comprises the written contributions of participants in a symposium held in Dallas, Texas, June 3-5, 1980, entitled "HAMSTER IMMUNE RESPONSIVENESS AND EXPERIMENTAL MODELS OF INFECTIOUS AND ONCO LOGIC DISEASES." This meeting followed its predecessor, "Hamster Immune Responses: Experimental Models Linking Immunogenetics, Oncogene sis and Viral Immunity" by three years. This more recent meeting was more pointed in its focus and the contributions appeared to be more tightly associated. These meetings are part of an extend d effort by experimentalists using the Syrian hamster as an animal model system to bring together workers in potentially related areas for the exchange of ideas and information. The success of the symposia derives partly from the scientific excellence of the contributing scientists, and partly from the financial support of the National Institutes of Health through the Fogarty International Center. The administration of the University of Texas Health Science Center at Dallas, under President Charles C. Sprague, also donated time, facilities, and financial sup port. Preparation of the manuscripts in this volume, as camera-ready copy for the publisher, was the diligent and dedicated effort of Ms. Sara Howard. Copy editing was expertly performed by Ms. Sandra Schulte and proof-reading was the responsibility of Dr. Patricia Fultz and Ms. Alix Gerboth. However, final responsibility for any errors and omis sions in the published volume is taken by the five local editors: J. Wayne Streilein David A. Hart Joan Stein-Streilein William R. Duncan R. E."