The role in immune inflammation of basophils, mast cells, and their contained vasoactive amines is most generally appreciated in immediate hypersensitivity reactions, such as allergic responses mediated by IgE antibodies. However, there is growing recognition of a role for these elements of immediate reactions in prolonged and delayed hypersensitivity responses in which thymus derived T lymphocytes (T cells) and anaphylactic antibodies are potentially both involved. Mast cells, whose origins are uncertain, are the principal vasoamine-containing cells of the tissues, while basophils are bone marrow-derived cells and are the principal vasoamine cells of the blood. In mice (which appear to lack basophils) the onset and full development of delayed type hypersensitivity (DTH) responses seems to require a critical communication from T cells to mast cells to vascular endothelium, via vasoamines. In humans and guinea pigs it is now recognized that delayed-in-time immune processes which are governed by interaction of antigens with T cells and/or with anaphylactic antibodies can induce basophils to leave the blood and infiltrate the tissues.