Inositol lipids have become a subject of great interest because of their central role in transmembrane signalling. The arrival of an external stimulus (eg hormones, neurotransmitters or growth factors) results in the hydrolysis of inositol to produce a neutral diacylglycerol and inositol triphosphate which is released into the sytosol. The inositol triphosphate stimulates the release of calcium from intracellular reservoirs and the diacylglycerol activates the membrane protein kinase C, which in turn phosphorylates various cellular proteins.