Almost 30 years ago RITOSSA described a new puffing pattern in salivary gland chromosomes of Drosophila following heat shock. This was the first description of a heat shock response. For years, development in this field remained modest and it took another decade before the relevant gene products-the heat shock proteins (hsp's)-were made visible by TISSIERES and co-workers. Subsequently, progress advanced more rapidly and we can now state that studies on the heat shock response have contributed much to our understanding of various principles in molecular and cellular biology such as control of gene expression and regulation of protein translocation. More recently, the study of hsp's has converged with immunology. There are several reasons for this: The chaperone function of certain hsp's makes them particularly apt for central functions of immunity, including antigen presentation and immunoglobulin synthesis. Furthermore, an effective immune response is often caused or followed by stress situations as they arise during trauma, inflammation, transformation, infection, or autoimmune disease. Due to their abundance during stress, hsp's can provide prominent antigens in many of these situations. This volume contains 11 chapters written by well-known experts dealing with various facets of the fascinating liaison between hsp's and immunity. The particular relation of hsp's to the immune system may be best illustrated by their intimate association with the major histocompatibility gene complex. Still, as discussed by GONTHER, the relevance of this fact to our understanding of hsp functions in immunity remaif)s speculative.