This paper considers the participation of macrophages, thymus-dependent lymphocytes (T-cells), and thymus-independent lymphocytes (B-cells) in man's immune response to malaria. Although phagocytosis by macrophages is an important feature of malaria the full extent of cooperation between these cells and T-and B-cells is not known. Evidence that T-cells play an important defensive role is at present unconvincing. B-cells on the other hand function importantly in the synthesis of immunoglobulins and specific antibodies and factors possibly influencing their activity are considered. Different epidemiological patterns of malaria antibodies in sera are described and the need for the routine inclusion of reliable antibody detection tests as part of malaria survey techniques, particularly where antimalarial drug usage is frequent, is emphasized.