Leukocyte culture conferences have a long pedigree. This volume records some of the scientific highlights of the 16th such annual con ference, and is a witness to the continuing evolution and popularity of leukocyte culture and of immunology. There is strong evidence of the widening horizons of immunology, both technically, with the obviously major impact of molecular biology into our understanding of cellular processes, and also conceptually. Traditionally, the 'proceedings' of these conferences have been published. But have the books produced really recorded the major part of the conference, the informal, friendly, but intense and some times heated exchanges that take place between workers in tackling very similar problems and systems and which are at the heart of every successful conference? Unfortunately this essence cannot be incorpo rated by soliciting manuscripts. For this reason, we have changed the format of publication, retaining published versions of the symposium papers, but requesting the workshop chairmen to produce a summary of the major new observations and areas of controversy highlighted in their sessions, as a vehicle for defining current areas of interest and debate. Not an easy task, as the workshop topics were culled from the abstracts submitted by the participants, rather than being on predefined topics. The unseasonal warmth in Cambridge was reflected in the atmos phere of the conference, the organization of which benefited from the administrative skills of Jean Bacon, Philippa Wells, Mr. Peter Irving, and Mrs.