This volume contains papers presented at the international conference on "Transgenic Mice and Mutants in MHC Research", held in Bar Harbor, Maine, in June, 1989. The meeting brought together eighty researchers working in the field. While mouse H-2 mutants have been known for many years their studies continue to contribute a great deal to our understanding of structure/function relationships and evolution of MHC molecules. Recently a new direction of research has emerged on regulation, expression and function of MHC genes using transgenic animals carrying exogenous MHC genes from the same or other species or engineered MHC genes. With the introduction of transgenic mice more specific questions about the various functions of MHC genes can be answered as, for example, the role of soluble and membrane-bound MHC molecules in self tolerance and elimination of specific T cell clones, recognition of human MHC antigens by the mouse immune system, the role of individual human MHC genes in disease susceptibility. New approaches for evaluation of the role of MHC linked and unlinked genes in susceptibility of mice to malignant tumors and their metastases have been also reported. Our purpose has been to provide a forum for discussion of these new developments. Many questions remain to be answered but the necessary tools have become available. We thank the contributors and hope that the readers will benefit from this Pro ceedings. We wish to acknowledge the financial sponsorship for the meeting by The Pew Charitable Trust and Howard Hughes Medical Institute.