AbstractFundamental research in immunology has led to significant advances in cardiac and other organ transplantation. Immunology has now entered the era of molecular biology and sophisticated techniques have been applied to an understanding of immunological events at a molecular level. Future progress in transplantation will be based on these advances in immunology. This is a review of recent work on the structure and action of cell surface molecules important in normal and abnormal functioning of the immune system. Present understanding does not permit a comprehensive description of immunology at the molecular level. However, the exciting developments taking place in fundamental immunological research hopefully will be a stimulus to new progress in cardiac and other organ transplantation.