Sphingosine 1-phosphate (S1P) is a lipid signalling molecule with Ca(2+) mobilising properties. Importantly for a role as a Ca(2+) release messenger, intracellular levels of S1P can be regulated by a variety of extracellular stimuli, via the enzyme sphingosine kinase. However, neither the mechanism underlying S1P generation, nor its actions at the endoplasmic reticulum are clear. Thus, the role of S1P as an intracellular mediator of Ca(2+) release remains in the balance.