The sea urchin egg has proved a reliable and robust system for measuring intracellular calcium release in response to three independent mechanisms: inositol 1,4,5 trisphosphate, cyclic ADP-ribose and the recently identified molecule, nicotinic acid adenine dinucleotide phosphate (NAADP). These calcium release mechanisms have been studied in homogenates of Lytechinus pictus and Spongylocentrotus purpuratus, which are two sea urchin species located off the west coast of the USA. A new calcium-release model from a species of sea urchin present off the coasts of Britain, Psammechinus miliaris is characterized and described. Although the Ca2+-release characteristics in this species do not differ from those of the other two sea urchin species, it may provide a more economical and convenient model for European scientists.