At fertilization in mammals, the sperm activates development by causing a prolonged series of intracellular Ca(2+) oscillations that are generated by increased production of inositol trisphosphate (InsP(3)). It appears that the sperm initiates InsP(3) generation via the introduction of a sperm factor into the egg after gamete membrane fusion. We recently identified a sperm-specific form of phospholipase C (PLC), referred to as PLCzeta(zeta). We review the evidence that PLCzeta represents the sperm factor that activates development of the egg and discuss the characteristics of PLCzeta that distinguish it from the somatic forms of PLC.