Injection of sperm extracts triggers Ca²⁺ oscillations in mammalian eggs similar to those seen at fertilisation. Here, we show that addition of sperm extracts to sea urchin egg homogenates causes Ca²⁺ release and inositol 1,4,5-trisphosphate (InsP₃) production. Furthermore depleting homogenates of phosphatidylinositol lipids using a phosphatidylinositol-specific phospholipase C blocked the sperm extract from causing InsP₃ production and a Ca²⁺ rise. A response could be recovered by the addition of phosphatidylinositol 4,5-bisphosphate to either sperm extracts or egg homogenates. These data indicate that sperm extracts contain an InsP₃-generating phospholipase C which may play a role in Ca²⁺ release at fertilisation.