The mast cell's association with asthma has a long history dating back to the turn of the century, when Dale and Laidlaw described histamine as a spasmogen for guinea-pig airways and a proposed mediator of acute anaphylaxis. Almost half a century elapsed before histamine was localised to the granules of mast cells, although the release of this and other mediators of the acute allergic reaction were known to involve reagin subsequently identified as IgE. The biochemical mechanisms involved in transduction signalling not only results in the calcium and energy-dependent release of preformed mediators by degranulation but also the generation and subsequent release of an array of newly formed products, many of which are derived from phospholipid precursors.