This volume contains papers presented at a symposium on "The Role of Lympho­ cytes and Macrophages in the Immunological Response" at the XIII International Congress of Haematology, Munich, August 1970. This symposium was designed to highlight current work submitted to the Haemato­ logy Congress which related to the role of cellular cooperation in induction and expression of the immune response. The symposium was divided into two parts. The morning session consisted of invited papers dealing with various general aspects of the field (papers 1 to 5) which were relevant to the afternoon session, which con­ sisted of free communications submitted to the Congress. In the discussion it was emphasized that whereas lymphocyte activIty ultimately underlies all immune induction, the cellular and humoral manifestations of the immune response are governed by distinct yet interacting compartments of the ly.mphoid system. Much interest centred on the role of thymus-derived lymphocytes as cooperator cells in antibody formation; and the mechanisms by which macro­ phages assist antibody production. The discussion brought together work on lympho­ cyte activation, the generation of lymphocyte activation products (lymphokine factors) and the cellular events underlying the induction and expression of the Immune response. The helpful cooperation of Springer-Verlag has enabled rapid publication of the papers presented at this symposium. London, February 1971 D. C. DUMONDE Symposium Moderator Contents The Spectrum of Thymus Dependency. E. LEUCHARS 1 The Flow of Information during Primary Antibody Synthesis. D. ]ACHERTS.