The phosphoinositides and their derivatives are ubiquitous cellular phospholipids that are important components of several intracellular signalling pathways. The second messengers derived from the breakdown of phosphoinositides, mobilise intracellular calcium and activate protein kinase C. In addition, by regulating actin-binding proteins the polyphosphoinositides play a pivotal role in platelet actin rearrangement, an essential step for platelet aggregation.